That is indeed the claim (deliberately buried). I’ve heard it many times. There must be a reason for the claim. Maybe just propaganda to stir intrigue?
The upright stones could be easily tipped over, which suggests that they were carefully buried after each period of use. That wouldn’t explain how, when a large crowd was around doing their thing, no one bumped the over and the whole bunch went down like dominoes, killing everyone in their path. Seems more likely that they were held in place by something no longer extant, such as a wood roof or just some organic glue or mortar that hasn’t survived.