It’s worth noting how overly simplified the idea of a “grade 1” or “grade 2” calf strain is. It works fine for explaining things to the media or in a non-elite athlete setting, but in reality there is way more nuance to it.Grade 2 calf strains happen all the time in the NBA. Typical recovery time is 4-6 weeks; and KD was right at 5 weeks when he returned. They (= KD and the med staff) may have been aggressive with the timeline, and may have assumed a mild risk of re-straining the same calf muscle, but did anyone think there was a real risk of a ruptured Achilles? I know they're in the same area, but is there precedent for a player returning from a strained calf and immediately tearing his Achilles? I dunno, I'd allow a strong possibility that we're dealing with a pretty freak injury that could have happened at any time, including during rehab.
With the improvement of MRIs and newer data (mostly done in European soccer players) there is now a lot more sophisticated grading for pro athletes. Lots of grading systems are 0-4, and then subdivided A, B, and C to better predict return to play. Some are more detailed than that.
The location of the tear and the length of the tear are critical, it’s not just mild, moderate, and severe for these guys anymore. That stuff works for your casual weekend warrior (no pun intended), but I’m sure the medical staff had a lot more to go on than that. If the tear was very low, near the Achilles, must have known there was some Achilles risk.
In the end, obviously they pushed things too much and it backfired. Valuable data point for the medical staff for future decision making (I’d love to see all of his mris!!), but devastating for KD.