We had a similar thing a few years ago at London Welsh. I'd taken 4 friends with me, 2 English, 1 Scottish and an Irish lass... I didn't realise they'd be the only 4 non-Welsh people in a 2000 people marque! Some welsh guy was being a **** for the first 20 minutes of the game (and 20 minutes before it started) until about 50 Welsh guys all started shouting at him... they all told him that he should buy us drinks for the rest of the day, which to be fair to the guy he did. Well until the last round of the day when we got him one back.
For most Welsh people, rugby is a huge part of the Welsh national identity, just like the giants foot prints making the valleys. There aren't many more passionate fans around for any sport even if we don't show our feelings about it that often.