Shit performance by Liverpool, nothing else to it.

I wouldn't say he's overweight. My guess he is still around that recommended 8-12% body fat region for a footballer. Also, in England lower league football is 90% fitness. There isn't much technique, so if he wasn't fit, he wouldn't play.
The fact is anything can happen in football. When a team like Liverpool plays inferior opposition, they must play full strength. They can never take a game as a given. That's partially what happened today, and Oldham punished them. No one else is to blame other than Liverpool.
Ok, here's the humorous side of this. With these 3 somewhat shocking results, some English football pundits have come up with the idea that Premier League teams have become to "continental" or "technical" to keep up with the rumble tumble style of lower league football.

I even heard some of them saying that they appreciate how English teams are adapting technical styles of play, but they wish that sometimes they'd just play more direct and grind it out. No wonder the English National Team is shit right now. They can't even see the problem with their players is lack of technical skills all around. They used to have that bullshit theory that Barca would struggle against teams like this. Barca would have won 10-0 today most likely. Liverpool just weren't good enough, and they were too complacent. Also, Jones and Coates had shockingly poor performances. This happens sometimes, but it was probably from being complacent on the whole. That's why they lost, not being too "continental" or "technical."