If she was HB8 no doubt she would have guys trying to sarge her all the time, and the thing is although you may of agreed up front about meeting another guy could have been right in front of her face who got in there.
I met a girl before who actually had plans for a guy to come round her place, but I somewhat gazumped him by arranging to meet her on the same day and showing up before he showed up, so she flaked him and well let's just leave the rest to your imagination
P.S Also when a girl arranges to meet for no strings, without sounding desperate its best to capatalise on it at the time it comes into subject, as if you arrange it for another day it puts too much pressure and expectation on it