I feel it could go both ways - they truly could just not like you, and that's how they are handling it (I do this with people I do not like, I have a very difficult time "faking" anything).
But it could also be the opposite - they are cripplingly shy around people they don't know very well. I know I personally am like this as well; whenever I meet someone new, I tend to shut down, avoid eye contact, avoid any potential for "small talk", things like that, and it's not because I don't like you necessarily, it's just because I'm uncomfortable in that situation. And if they are chatty and open with others, it's possible that they are closer to those others and therefore more comfortable.
It could be both; but if they are a normal regular person, it could unfortunately be that they don't like you. However I too am very bad at reading people, and often times I will take these kinds of behaviors as negative, when in fact it's just someone who is uncomfortable around new people. It's rare, but I know it's possible because I do it myself.
Just continue to be kind and polite - that's the best way to handle it I think.