As it turns out, Manziel's reason for leaving was illness, according to a statement from a camp spokesman.
Even Peyton Manning himself defended Manziel:
"I enjoyed meeting Johnny. I can remember a 20-year-old Eli [Manning] missing a meeting [at camp] and catching some flak. We always have counselors who leave early. Johnny was great with the campers for the time he was here. He had to leave early. I wish him the best and I want him to come back as a counselor next year."
It's nice of the Mannings to cover up for Manziel, but based on photographic evidence, Manziel was definitely out partying with Alabama QB AJ McCarron on Thursday night, before showing up late to camp activities on Friday.
So most likely, Manziel was hung over, or simply slept in, and that's why he was late.
The real question isn't whether or not Manziel's reasons were valid, but rather whether it really matters.
Pretty much everyone has a little too much fun in college, and many people still manage to make something of their lives. Even President Barack Obama has admitted to a little recreational marijuana use when he was younger. I'd say he still ended up doing pretty well for himself, so a few nights of partying for Johnny Manziel in the offseason probably won't destroy his career.
We can overreact, we can play the "what if?" game, or we could just realize that his NFL future depends very much on his ability to develop into an NFL QB, not his recreational activities off the field.
Johnny Manziel needs to learn how to concentrate on becoming a pass-first QB, tighten up his delivery a bit, and work on looking off coverage. That's how he'll make himself into an excellent NFL prospect. The rest is just a distraction from one of the better athletes in all of college football.