If it's a guessing game we're playing, I'd guess Andre Smith too ... very odd to abruptly leave the combine like that, and it's what I immediately guessed when he did it. The only reasons people leave stuff like that abruptly that I know of are:
A) Death/Pregnancy in the family,
B) Injuries (which always get reported immediately)
C) Legal problems,
D) Substance problems,
There was no injury report, no police report, and in my mind that leaves 2 alternatives, death/pregnancy in the family, or banned substances. I guessed then it was steroids, so I'm sticking with that guess now ... but it is ONLY a guess.