Post hoc ergo propter hoc
Two guys I played footy with had a similar thing, where they had a flow on injury to a seeming unrelated part that was caused because their body had shifted its biomechanics to compensate for the lameness from the injury, and when they ramped up training loads without sufficiently correcting that imbalance, it means the strain caused a new injury.
Who are we to know? But saying this is a surprise because it’s a different injury in a related area is pretty naive. It’s like saying he only ever bet on footy and lost all his money, so it’s a total shock that he bet on the horses and lost his money. They couldn’t possibly be related..