There could be various reasons for that.
It more than likely indicates that the conditions he is being kept in at the petstore are not completely suitable. If a chameleon indicates that he wants to get out of his cage, he is probably not happy in it. There might be something he is trying to get to (e.g. water, food, heat, or most likely - space - if there are a lot of other chameleons in the cage with him).
They are neither friendly nor unfriendly. He probably sees people as a route to get out of the cage - he is not trying to make pals.