What to make of this?

Quick summary: There are two girls. One comes over and compliments my attire, engages in flirty banter, then leaves to go back to her girlfriend (just barely within earshot) and proceeds to tell her what I said, to which they both proceed to break out into that stereotypical giggle patented by grade schoolers.

Ok, cool. But what the hell does it mean?

Overthinking? Or should I assume interest? And if the ladder, on who's part? The girl who approached me is known for being more assertive and playful. The girl who stayed back is the more reserved of the two, but I've suspected she's had feelings for me for some time now.