Thanks. The technologies page talks about selection, mainly: (1) either Alexa top 10 million or Tranco top 1 million; (2) only apex domains are counted. It doesn't talk about weighting at all, so coupled with the subdomain policy, a reasonable assumption is that the statistics are not weighted at all.

The disclaimer page also makes it clear that they don't analyze anything that requires interactions like signing in. Together with the subdomain policy, I suspect for any business where the landing/marketing site and the core business offering differ in technologies used (which is especially common for SaaS products), they will only pick up the marketing site. They also seem to allude to some sort of webmaster self-reporting mechanism though, not really sure what that means.