What does it mean when a guy playfully "scares" you?

So this guy I'm friends with will come up behind me and "scare" me, by grabbing my shoulders then giggle/laugh afterwards, but never in a malicious way, always just playful. While I was kneeling on a dock he came up behind me grabbed my waist and pretended to push me in, of course he wouldn't actually let me fall, but he does this a lot. I was watching a scary movie with him and he did it at least three times during a 30 minute period... I also know he is a shy/introverted person, but I'm not sure if that means anything.
He's flirting
He's being a guy
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We were actually sitting shoulders together alone on a couch, that could have fit four, for like two hours until 3am. I probably should have included that too lol...
What does it mean when a guy playfully "scares" you?
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