Well it happens a lot with NTs even if your not friends and you should be careful to take this too literally. Sometimes when NTs are being friendly, they might suggests trying to get to know you and perhaps "become friends with you". But then you might not necessarily be friends yet. Especially when its a group thing. Its their way of trying to include you. So they might not actually consider you a friend, but either way if there trying to hangout with you, they're trying to include you. its a subtle gesture towards friendship. Or they might think of you as a friend. Sometimes when you get "in" with a group of NTs, they oppotunities to hangout and do things are so much greater cause NTs like to hangout in packs.