I'd like to offer my perspective, based on the also very interactive and social board games - which I also enjoy immensely.
If you sit around a table in a competitive board game and one of the players donates in a fairly one-sided way to another well... sorry man, but you're skewing / ruining the game. Ergo multi-boxing.
BUT...
and here I'll mostly highlight what others have said previously here :
- Subterfuge plays on much longer timescales, so your "multiboxing" (heavy inverted commas, please note) can be countered more effectively (increased reaction time, more alliances, etc.)
- because of the previous point, you may also have an endgame where you still finish on top, instead of just committing to donating to the other fellow. You may communicate to that effect wisely to get others on board
And more importantly... I wouldn't play board games with a rude stranger like you described. So in a way he does get what he deserves
It is a matter of perception. I'd probably target you right away in a game if you did that, but trust me the rude dude would get axed next.