What does it mean if your crushes best friend calls you your crushes girl?

So today I was at a football game for homecoming and I was just talking with my friends goofing off, (no my crush wasn't there at the time) and there was this one really desperate guy (no offense he just asks out a bunch of girls) that kept trying to get someone to slow dance with him. As soon as he saw me he asked if I would slow dance with him, which I was hesitant to answer, it's like a your cute but would I even date you? Moment, then all the sudden my Crushes best friend steps into the conversation and says Aye yo that's (my Crushes name)'s girl! And I was so confused; we've never officially dated, I mean we talk a bunch, which ig could be called flirting, and I know he talks about me a lot, I mean I do too, but I can't help but wonder what this means; was it a joke? Or was he serious? ( Everyone basically ships us, even his twin sister)

What does it mean if your crushes best friend calls you your crushes girl?
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