He likely had predisposing genetic factors.
Screening is the future.
very possibly...
As I said though, this will become more common because of the number of absolutely humongous human beings in the NFL. Maybe (hopefully) not as young as this, but when they get older and retire.
It's in my future two weeks from Friday. There is no good reason for adults not to undergo vascular ultrasound screening. It's cheap, painless, and takes no more than an hour.