Not believable. That other pedo would have beaten him to pedo death.
shareAlso possible that the hackers didn't intend for either one of them to die, just for them to get beaten badly. Perhaps during the fight they messaged the larger one to stop. Especially since the hackers needed them alive to experience the final punishment of having their secrets revealed (like they did for every one else).
shareAm I the only one who noticed that the bigger pedo was drinking? He didn't seem to be in a very good shape, either. I'd say fighting to death and drinking don't mix well.
At that point Kenny was sober, lucid, and maybe a bit angry and tired of the whole situation. Someone in his situation could show an unexpected strength, especially with an adrenaline rush. Also, we had been shown him as a young, innocent kid who just got caught jerking off in front of the computer, then suddenly we discover he is a pedophile. Maybe he was also more violent than we would imagine.
Anyway, I think that showing the other guy drinking (and he might have drank enough while waiting for Kenny) was a hint at how he was beaten by an apparently weaker opponent.
Personally, I'm great at fighting when I'm drunk!
However, your points are very salient and I agree completely. The older pedo had a typical pedo-looking body (of the type you might see on Chris Hansen's show). He had weak feeble little arms and was gangly with a complete lack of shoulders (perfect for molesting and clutching unsuspecting children, but bad for fighting). The kid appeared to be an incredible pansy as well so I'm coming up blank with a believable explanation on how he overpowered a similarly weak, albeit heavier pedo.