That is because when they initially assessed the great former Ferrari and Mercedes driver, he was conscious.
A senior emergency doctor was quoted by Stern as saying a "confused" patient who nonetheless has "his eyes open" and is "speaking and moving", can initially be diagnosed as having a less severe trama.
But in a small group of patients, the situation can "deteriorate rapidly", Stern added.
"Had the rescuers arrived at the scene minutes later, they may have recognised the matter of life and death," the magazine reported.
In reality, Schumacher was initially flown by helicopter not to the specialist Grenoble hospital, but a smaller facility in Moutiers.
There, the 45-year-old was initially intubated, but he had already lapsed into deep coma.
So he was flown a further 20 minutes to Grenoble, where upon arrival a local journalist observed that the helicopter paramedics were "noticeably excited".
Schumacher's manager Sabine Kehm would not comment, but Stern suggests that the great German's prospects might have been "dramatically" improved had he been ventilated and operated on sooner.