Yep, sectarianism is habitual in some. So these guys are perceived as rich Protestants. Therefore working class Catholics are more likely to criticise them, meaning some (not all) Protestants want to defend them (sort of on the principle that "the enemy of my enemy is my friend).
Some of the more, erm, assertive FB and twitter crap makes me wonder if the girl is Catholic, and therefore seen as somehow "lesser" by a proportion (and thankfully an ever-decreasing proportion) of the population
The sectarian issue in the north is a little like a race issue in other countries - so if this had been, say, rich white frat boys in the US vs a poor black girl similar lines might be drawn by some onlookers 