Heat of the moment more likely. Us men however we deny it are susceptible to drastic measures when we're desperate and backed into a corner, sometimes (as in this case of the fucking idiot who thought it would be actually nice to dupe a fellow gambler off of his fair share of win) we even cause these drastic situations to come around. But the thing is, most of us right here wouldn't even dare get into fights like these let alone get into an interaction that would lead to an altercation of sorts. Dare I say we don't even have friends to do this with cause we're either embarrassed to barge them into this thing/hobby of ours, or we just suck at socializing, so while this is a general possibility through and through, I don't think this is something that happens everyday.
To be honest, it's not always about being social or having friends to do such kind of partnerships with, but it also depends on one's personal preferences when it comes to things like this. I, personally, would never want to involve someone else with me betting on a game even if I know that it might be a sure win and I might get more money if I get someone to invest with me, but I know that things don't stay the same once the money comes in.
Even the most loyal friends can become enemies because of money, so such things do happen no matter how good or bad someone is, that is why, it is simply better to do your things yourself and even if you decide to have a partnership, negotiate the terms before and do it in a legal way by writing them down and taking signatures of both parties so that there are no extra things brought up later on.