Patella tendon ruptures are infrequent, particularly those that have a complete tear. Considering that Lin still walked (mostly) by himself to the locker room, this doesn't look to be the case.
This used to be a career-changing injury back in the day, particularly in the Philippines (Samboy Lim and Chris Calaguio are examples). These days though, thanks to stem cell treatment and bioengineering, a full recovery is actually possible.