Why would a man use the 'eyebrow flash/raise' when parting company/saying goodbye to a woman?

Usually on greeting someone the eyebrow flash can be a signal of attraction or liking a person. What does it mean if it is given at the end of a conversation where he asks to see her again in a month?
Why would a man use the 'eyebrow flash/raise' when parting company/saying goodbye to a woman?
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