It’s probably showing a “recent reviews” window. The overall has hovered between 69-70 since release. Since the number of reviews in the window is small, a few negative ones dropping out of the window and a few positive ones being added makes a huge difference.
There was definitely a PR push to get positive reviews in response to alleged “review bombing” (which seems to have consisted of one inappropriate review that was removed).
Looking at the page the “recent reviews” total 30, so it takes just a couple of reviews to create that kind of % shift.