I understand your point about not assuming this concerns alcohol.
But on the other hand, teams regularly wind up with players who had huge red flags hidden from them. Or, the problems were blown off as college kids antics that would get left behind. When in fact there were serious and deeper underlying problems that surfaced once they were put on an NFL team, and weren't babysat every day, and once they got a nice wad of cash to spend. And, sometimes, when they suddenly were faced with pressures they had never had to face before as college athletes. In other words, they are expected to be responsible adults and they can't hack it.
So, until proved otherwise, and considering what has been widely publicized about Bennett when in college, I still think that issues with alcohol....maybe with mental health....are the leading candidates for his mysterious "non-sinister" absence . But.....this is (as I've said) only my opinion and speculation.
And that sinister is a very strange word to employ.