Uhm, people don't even need to speculate on how much other hodlers hodl. A certain someone already openly stated that Trendon Shavers alone cost him 1.6K BTC, and that's after deducting "interest" received. So the principle amount is even higher. No need to read up past posts either. People can also make educated guess simply based on the year that they started accumulating BTC, assuming that they hadn't lost it through the million ways that you can lose your BTC.
Yup. It is pretty easy to come up with a ballpark figure with a high probability of being correct. But also there are many additional factors that could make that guess completely wrong such as extraordinary loses, sodls and also people giving out inaccurate/false information about their hodlings. So, in the end, it is just pure speculation.
I, for one, have said in the past that I am into double digits BTC... but that could have changed or even be a completely false statement from the beginning.... which might even be a good opsec for some big hodlers btw.