Do guys mumble if they like you?

So there's a kid in my class that talks to everyone around him like a casual dude but I noticed that whenever he's around me he starts to do this weird mumbling thing. Like one time I was standing and waiting for the teacher to unlock the door. I heard the door open so I turned around and he was standing right behind me. After I turned he started to mumble something but I didn't know if he was talking to me so I just ignored it. I was thinking maybe he's shy or something but then I remembered that he talks to everyone else with no problems.
Do guys mumble if they like you?
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