What I've seen is a newcomer make some shaky or flat wrong pronouncements and get called on them. Then instead of rethinking their position in light of the contrary evidence, they get their back up and become argumentative. The so-called "ganging up on a newbie" follows.

If you tell a room full of people that 2+2=5, get corrected and start to argue about it, is it ganging up if most of the people in the room call you a dope?