I don’t know how many users they have either, but re: whether it 100k reviews total last week.
Normally I think you could expect only a few percent of your users to leave reviews.
If you then piss off your whole user base collectively with actions that are unfair to them, then it is not a valid argument to say that because there are more reviews that the reviews cannot be real.
I am not saying that all of these 100k reviews are real. But I am saying that how many or few reviews they had before does not count because until you do something really bad or something extremely good 90-99% of users are not going to leave a review.