Anything is possible. You can never prove anything. In science/real life true means very likely and false means very unlikely. So yes the simulation could be wrong, but I guess with everything we know and the error bars the answer was clearly no.

Following up with "Thus, the regular sizes of planets is a real astrophysical pattern" seems particularly premature.

The answer is "no" because the author needs to come to a conclusion for the paper that they are writing. It doesn't matter if they are correct, it matters that they produce a paper, so that's why they came up with this conclusion.

I wish researchers weren't biased to produce papers, it doesn't help us with honestly understanding our universe.