Hi there. Welcome to
SLU. Beware of elder gods.
I have a llama.
Now that we have that out of the way, I'm not seeing where being a stranger and getting a "who are you?" = clique. Its a valid question in that case. I would say that the onus is on you to post, introduce or in some other way make your presence known.
A clique, generally, is, well to take the dictionary.com definition: "a small, exclusive group of people; coterie; set"
We are far from exclusive as this board welcomes generally anyone at any time. Anybody can make an account here, anyone can post and say hi, anyone can say pretty much whatever they want with very few restrictions.
If some folks were having a discussion on the street and you wanted to chime in, you wouldn't just walk over, but in and offer your unsolicited opinion. If you cared enough you might walk over, say 'excuse me' and introduce yourself, and then say "i couldn't help overhearing your conversation but ...." Especially if that group was a 'forum' where others were more or less invited to do that.
Regardless of the shouting matches around here, I fail to see why manners and polite social norms are ignored and those who have done so labelled as cliquish when they turn and stare blankly at the stranger who offers his or her opinion after failing to introduce one's self.