Honestly.. What does it mean when A Guy say, " That's my Boo"? We aren't official why is he telling mutual friends that I'm his boo?

me and this guy have been talking. And apparently him and a mutual friend of ours was having a conversation and I came up. And he said my name, then said thats my boo. and my friend said thats a good boo to have.

Ps: me and this guy have been talking and taking things slow we only kissed before thats it.
Honestly.. What does it mean when A Guy say, " That's my Boo"? We aren't official why is he telling mutual friends that I'm his boo?
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