That policy would make sense, but that involves major caveats that aren't clear from the original description. That works because it's specifically written with "generosity buffer" that (by design) only benefits your grade, and thus doesn't indicate the teacher was falsely labeling the answers as correct when they weren't.
That's not the same thing as the original, which implied "my grading is so random, hope you're lucky on the rescore".
Edit: I had a high school teacher with a policy where she’d add X points to every score from the get go, and you’dlose those if you objected to grading, so you’d only object for misgrades by more than X. But that’s not the same as the original “okay, let’s roll my truth-recognizer dice again!”
Meanwhile, in a less politically charged situation, it's pretty normal, or at least smart, to go back over any area where you messed up with a fine-toothed comb.
If, and this is a rather pessimistic assumption, if the student is likely to lower their grade on a re-test, in my experience it's more likely to be because the original grader was being generous in the face of ambiguity, rather than systemic random errors. That's because the graders are mostly nice people. If that's not good enough for someone, they damn well better have a good reason for it. I have no problem with policy that enforces this. The politics are a distraction from the ethical question.