What does it mean when someone suddenly starts being nice to you?

I got into a fight with someone and we didn’t talk after a long time (about two months). Last week this someone started being nice to me suddenly and started talking to me first after saying there’d be nothing to do with me anymore, how should I react? Or what should I think?
Would it be bad if I asked them why the sudden niceness? Or should I just not think too much about it?