They’re making the (possibly false) assumption that density will stay the same, so size must grow with weight.
Of course, it’s equally likely that size will remain constant. It changes or it doesn’t -> 50/50 odds. Until the point it all collapses into a black hole.
Those are fun! I went to 4 or 5 of the Harry potter movies in concert. It’s a fun way to re-watch older movies on a projector above, while having an amazing live orchestra play through the whole movie. It’s really cool that the orchestra director can follow along with the electronic karaoke-like metrenome and keep everyone in sync with the movie the entire time.