Montgomery said he was unsure how close the ball was to the goal line when he elected to the run it out with 2:09 remaining. The 25-year-old Montgomery was two yards deep in the end zone and reached the Packers' 20 before Ramik Wilson punched the ball out.
The Rams ran out the clock to preserve a 29-27 win, leaving Aaron Rodgers on the sideline.
"I had a returnable ball," Montgomery said, via the Milwaukee Journal Sentinel. "So I made a split-second decision on, I don't know if this is going to land on the goal line. So I'm not going to take a knee on the goal line, at the half-yard line and take a chance at putting the game in the ref's hands.
"Unfortunately, I ended up fumbling the football. I don't think we'd be having this conversation if I didn't fumble the football because we know how good our two-minute offense is. But I've never been a guy to completely disobey what I'm being told. I think you can ask a lot of guys in our locker room. That's not what I do. That's not the type of man I am. That's not the kind of person I am."
The NFL Network reported that more than a half dozen Packers players and coaches noticed Montgomery throwing a "tantrum" on the sideline after being removed from the game during Green Bay's previous offensive series. The Packers' decision to remove him from the game perhaps led Montgomery into deciding to return the kickoff, according to one player.
"They took him out (the previous drive) for a play and he slammed his helmet and threw a fit," the player said. "Then (before the kickoff) they told him to take a knee, and he ran it out anyway. You know what that was? That was him saying, 'I'm gonna do me.' It's a (expletive) joke.
"I mean, what the (expletive) are you doing? We've got Aaron Rodgers, the best I've ever seen, and you're gonna take that risk? I mean, it's '12'! All you gotta do is give him the ball, and you know what's gonna happen."
Montgomery told reporters he was frustrated by the team's decision to pull him from the game, but said it had nothing to do with returning the kickoff.
"Absolutely not, and that's the point that I was trying to make," he said. " ... I'm very disappointed in the fact that was said and they tried to make correlations that don't exist."
Montgomery also said he was frustrated over the anonymous comments made about him after the game.
"We talk about being brothers," Montgomery said. "We talk about being family and keeping things in-house, in-house, this, that and the other. That's not what happened. I don't know. Maybe that's what they do in their family. That's not what I do in mine. No one ever said anything to me.
"No one ever came to me. So I'm thoroughly disappointed in the speculation and just the backlash I have to deal with now. Because now, we're talking about my character. We're not even talking about the fumble anymore, we're talking about my character. We're talking about the reasons why I did what I did, and I'm not OK with that."