Just read this article and I wanted to call BS on your criticism here. He never claims to adjust it to match the population. He just said there was an obvious bias, and then rotated the distribution to compensate for it. I don’t think he made any wild claims, as you say (or maybe I just didn’t see them).
However, I think the bias is there not because BGG’ers necessarily like heavy games more. I would argue that heavy board games have fewer plays and fewer ratings than lighter games, and that the people that play them (and rate them) are more biased than the multitude of gamers that play lighter games. Its why many limited-screening ‘artsy’ movies often have inflated scores on IMDB and many indie games have higher scores on Steam.