People flirt because they are flirtatious, not necessarily they think you are the one they should be with. You just are above a certain "least number of qualities to flirt" that's all I think. I mean he or she may well be treating you just like a statistic rather than an individual. All I'm saying if sufficient "above the bar" personalities are around then that person will flirt with all of them if the desperation and the context permits because not everyone flirts with everyone at the same time openly. They have mental models where they flirt with a particular person in a particular setting and with another particular person in another setting, maybe openly or privately but setting is different