Oh No not my gorgeous lad, he's still so lush
I've not had any experience that i can recall of just tendon damage so wouldnt have known although i'd have suspected perhaps yes.
However good to hear that he's getting better, i would say soft tissue injuries (& bones I suppose to a degree) normally heal so quickly in cats.
My guess would have been he'd jumped down onto the lid of a tin can / sharp metal / wire / slate etc or perhaps glass as you say.
Please give Red an extra pet from me when you next see him