It’s mostly the difference between police reported numbers and the ones from organizers. For Hamburg the police number is 50k, while the organizers said 160k for example. That’s why they wrote “more than 100k” everywhere. But I agree, that it’s really lowballing the extent of the demonstrations.
Still, even if we take just police numbers, Then bremen (45k) and hamburg (50k, massive lowball) already reach pretty much 100k. if you take into account all the other 20k+ demonstrations happening, and the other really big ones like berlin and munich, this isnt just a conservative estimate, its outright dishonest