The Heisman Trophy winner was a counselor at the camp for high school prospects run by Archie, Peyton and Eli Manning in Louisiana, along with many other college quarterbacks. He left before it ended last weekend.
"I was not asked to leave. It was a mutual decision," Manziel said Wednesday at SEC Media Days.
He said that while there were social events every night with the Mannings, he did not miss his meetings because of too much partying.
"The speculation of me being too hung over and that's the reason I missed the meetings is absolutely incorrect," he said.
Manziel said he fell asleep without setting his alarm and his phone died during the night. He said he was rooming with Alabama quarterback AJ McCarron, but that McCarron didn't wake him up.
"I'm definitely not going to pin it on him," Manziel said. "It's my fault - 115, 120 percent."
The 20-year-old faced hundreds of reporters during Wednesday's interview sessions. Wearing a dark blue suit, the 6-foot-1, 200-pound sophomore discussed his fame, decision-making and even answered a few questions about football.
He says his eventful offseason has been at times "blown out of proportion," though he did acknowledge that he needs to make better decisions because he's such a public figure.
"My offseason, all the stuff's that's gone on will have no effect on this season," Manziel said. "I'm ready to stop. No more talk after this. Let's play football."
Manziel is the first freshman to win the Heisman and undeniably a unique talent on the field. He led Texas A&M to an 11-2 record, including a 6-2 mark in its first Southeastern Conference season.
Second-year coach Kevin Sumlin's hurry-up offense was a perfect match for Manziel, who finished with 3,706 yards and 26 touchdowns passing and 1,410 yards and 21 touchdowns on the ground.
His 5,116 total yards were an NCAA freshman record and No. 9 on the NCAA's all-time list.
Sumlin and Texas A&M defensive back Toney Hurd Jr. both had praise for Manziel on Wednedsay.
"Johnny Football is a great guy," Hurd Jr. said. "He works hard. He's dedicated to his craft. I can't make any predictions on what he'll do, but I can tell you if you want to stop him, you might want to put 22 men on the field.
Said Sumlin: "I think (handling the Heisman spotlight is) a learning experience, a growing experience, because, quite frankly, it's something that nobody's ever been through at that age."
Mississippi quarterback Bo Wallace was also at the Manning passing camp and said the other quarterbacks enjoyed their time with Manziel. Wallace said Tuesday Manziel is "a fun kid" and "may catch more slack than he should."
"It's difficult - you want to go out and do 20, 21-year-old things," Wallace said. "But at the same time, you've got to know that you're the face of a brand. Ole Miss is a huge brand, A&M's a huge brand and you've got to have that in the back of your mind with every decision that you make."