Thought the same, from the screenshot it looks like he could’ve been waving and people take it out of context. After watching the 38sec clip I’m not so sure anymore. He does it on purpose and as an isolated move. He even repeats it.
At the very least it’s very strange gesturing. I don’t think you do a move like this by accident though.
Playing devil’s advocate: Perhaps universe as in “look up, it’s the stars”? I think it’s plausible, many children in that age also know about astronauts and aliens already.