Lemmy has about 50,000 users, similar to Kbin, but it’s users are commenting 120 times and also posting 16 times each a day on average? That seems unrealistic.

I think there might some confusion in your comment. The post’s data is for all lemmy instances, which is larger than just lemmy.world.

As of this moment, lemmy.world has about 51k users, followed by lemmy.ml’s 39k and beehaw.org’s 11k. If you take the top 10 non-bot lemmy instances, they add up to roughly 136k users. And that’s just 10 out of 1000 instances. Source: https://the-federation.info/platform/73

All of that to say your math might be wrong.