I think this can be the case sometimes, like with the people you know, rdgrad. I also think sometimes it is true that we think we like someone at first, and then in the friendship or relationship, we see that we actually do not like them much at all, and so we end the friendship / relationship, or distance ourselves.

I think in order to be able to tell if the person means it or its just a defense mech, one would have to observe the behavior of the person, like what you have done.