Re: Clarification
Isn't it just like saying "we won the war" when you were never a part of it. You identify with that team/community so you feel their victory is yours.
I personally don't watch football, I tried to as a kid but couldn't stand it for more than a few minutes, but I wouldn't say it's weird. Especially not when your hard-earned money goes on to buy your favourite team-branded clothes, season tickets, and whatever else that would go on to support them (i.e. their inflated salaries).
Arguably, one could say exclusively shopping at Asda would mean you should therefore see their success as yours, but that sounds silly.