If an outgoing guy calls you his sister does that mean he wants to be strictly friends?

Yes, that means that he doesn't see the girl as anything more than that of a sister..which means not sexually or maybe not even physically. But then again, he may feel very connected emotionally and doesn't want to ruin that, so giving the name as the "sister" in a way means that he cares so much about her that he wants her to stay in his life and doesn't want to cross the line of friendship and potential girlfriend.