Thank you for the link, but I am already sufficiently familiar with the definition of the word.
Arguing from your own copy/paste-
As a retroactive implementation of a per-account housing cap would serve as neither a form of retribution nor penalty through judicial procedure, then the only means you have as defining it as a 'punishment' would be your third option: 'severe, rough, or disastrous treatment.' That one, I am afraid, ultimately comes down to a matter of opinion.
I do not think that stripping excess houses would be 'severe, rough, or disastrous' as long as the owners were warned ahead of time, compensated for their purchases, and given time to decide what house to keep. You, obviously, feel differently. There is no objective way to determine which opinion is correct, so I guess we just have to agree to disagree on whether or not the term 'punishment' applies.