Was he scared or was he sad? He has no reason to be scared of the event, but I can understand being saddened by it, such a massive event that will change the look of the sky, potentially destroy the solar system we call home, (I'm less optimistic than your video,) and the fact we probably won't be around to see it?
It makes me sad at least.
A seven-year-old is not likely to understand the timescales involved.
Likely? No. But its certainly possible, and I do not know the child, so I can not make an assumption.