I have consolidated a list of three possible reasons women say this line to a man who asks her out on a date.
One, either she is not interested in you at all; and she is too cowardly and too dishonest and too low-quality to be real with you, failing to respect your time, emotion, etc. She knows full well ahead of time there is no possibility, but leads you on anyway to let you down “soft” after she has built you up.
Two, she finds you attractive but isn’t interested in romance with you… women like this enjoy having men at their feet, wanting to be with them. They enjoy the ego stroking and the sexual validation of having numerous suitors, and play hard to get when she is impossible to get. These sorts of women have many male “friends”, all of whom want to be with her. In fact, she has so many friends that she will reject any man who offers strict platonic friendship on account of having “too many friends as is”… when in reality she is rejecting your platonic friendship on account it doesn’t validate her sexually and on insults her ego to know and be reminded of the fact that you are not interested in more. She rejects any mans offer of friendship and offers friendship to any man who wants romance.
Three, she is interested in you romantically, after all. But she is too busy sluttily playing the field without actually having sex. She calls it “hanging as friends” when in her mind its “dating without commitment or monogamy”. She enjoys “dating” multiple men simultaneously while she decides between the two (or more) of you. She rationalizes this behavior so as to not feel like a slut, and she does so by calling it “friendship first”.
I suppose there is the possibility that she is interested in you romantically, just doesnt want to appear too eager either. Its still deceptive, though. The question as this point is, does she have other prospects, suitors? Has she been on other dates recently? And very importantly, did she go out of her way to insist that it wasn’t a date?