"hun" is mn argot for txtspking persons, who used to be found mainly in the exchanging pram part of mn.
I'm not keen on the term, myself.
It quite categorically isn't inflected with the Prot/Catholic thing - mainly because (I suspect) most of the mn-ers who brought the mn-hun into play were well too Southern to have come across that particular usage of the term.
I do suspect it has a vague nod to the "Hun" that were the scourge of Christian Rome, however. I think the term is supposed to be a humorous bringing-together of incongruity: groups of pram-wielding fluffy txters advancing like a nomadic horde on Rome.