If they meant this to be a kind of Extended Test, they should have written, that is an Extended Test with a Threshhold of the damage the patient has and that in contrast to a normal Extended Test hits that you collect do count, even if you didn't reach the Threshhold.
Also as already quoted the example would be wrong and nobody thought of the consequences, if you connect a rule that says that natural healing cannot always heal somebody completely with a rule that says that magical drain only gets natural healing.
Unfortunately, a sloppy use of a defined term like Extended Test, a wrong example and a not thinking through the consequences of two rules connecting seems to be quite possible with Shadowrun.
I personally have no problem with Body 1 and Body 2 characters not being able to heal to complete health without medical assistance and/or Edge and/or magical healing.
But then you have to rule, the only Medkits do not affect magical drain, but medical assistance that takes days does help.
Here is some longish guesstimations how a system with Extended Tests natural healing works:
(I call the last 2 rolls of an Extended Test (only 1 and 2 dice) Very Dangerous Dice and the last 4 (4,3,2,1 dice) Dangerous Dice because of their high critical glitch chance.
1 Body : the patient is very old and/or frail and/or sick, can roll only the Very Dangerous Dice and has only 3 percent to heal 3 boxes, never more. On the average he will have 1 box healed, but probably lower because of the high critglitch chance (I think it's about 27%), where he will be worse after healing, because of the 1D3 critglitch damage boxes.
2 Body: low constitution, can only roll the Dangerous Dice, with extremely low probability, but possible (about 1 in 60000) the patient has all dice hits and heals 10 boxes (shot within 1 box of instant death, first aid only stabilized and he then fully heals just by resting 4 days) , on the average he will heal 3 boxes, or less, if he is leaving the Very Dangerous Dice aside, because he doesn't want to risk critglitch)
3 Body: average constitution, can leave the Dangerous Dice aside, if he wants, and has still 5+6 dice left. Heals about 4 boxes when not using the Dangerous Dice and up to 7 when using them, probability of being worse after healing is very low
4 Body: some better than average constitution, can heal about 9 boxes (26 dice) without the Dangerous Dice, more if he risks them. This guy has a high probability to come back fully healed from being shot, stabbed, poisoned to within one box of damage of instant death, and all he has to do is rest 8 days.
5 Body: very fit, without the Dangerous Dice the patient has 45 dice to heal with 15 boxes on the average. Being shot to near instant death with 15 boxes of damage he can normally heal them all by lying on his couch for 10 days.
For those with Body 2 and more they might add the Try again rule, that allows a test to be repeated with -2. In essence this would be adding the stuff you would have had, if your Body was one lower in the list above. For people with Body 1 this is of course impossible, for Body 2 it's very risky to go another round with -2 and for Body 3 it begins to be interesting.
If you add somebody with Logic+Medicine this helper gives +1 die for the patients natural healing per 3 dice he has in Logic + Medicine. In a way this means, that per 6 dice in the helpers Logic+Medicine the patient heals as if he had one Body more.
So if you have a beginning doctor with Logic 3 and Medicine 3 help the Body 1 patient, you can look up the result what happens to the Body 2 person. If the doctor is very good with 12 dice (like Logic 4 and Medicine

the Body 1 patient behaves like Body 3 and can fully recover from a lot of punishment even though he is very old/frail/sick. If you have one of the best doctors in the world with 18 dice (Logic 6 + Cerebral Booster 3 + 9 Medicine) the Body 1 person heals/recovers like Body 4, so he can come back from 9 boxes of damage (as near to instant death, as he could be) to full health. But only with the very best doc.
This all is leaving gear boni aside which a fully equipped hospital may give (don't know the SR5 rules for these yet). You probably need the boni from the Medkit/Autodoc/Hospital to counter patient's implants and/or being a magician.
So if somebody with Body 1 or Body 2 get hurt they cannot fully recover without medical assistance. I have no problem with that. These are not stigmata, but rather a limping, a damaged organ, that could not be fully repaired, scars that still hurt etc.
In world where you just have to rest for x days to heal anything, no matter how bad, what do doctors do? Why are there still hospitals?
By the way, putting together these thoughts, another problem occured to me, if one says that the mage cannot use any medical assistance: do Trauma Patches work? If they don't work and First Aid is not allowed, mage who are bleeding to death will never saved. According to the rules, a character with Overflow can only be stabilized by outside sources and so people can say that this is not natural healing and so Stabilization would be a no-go for magical drain.
Of course I don't share this opinion, but the door for this interpretation is open.