It's not possible for an app publisher to delete reviews. However, in the Google Play Console, as an app publisher you can flag comments as against the Google

It's not possible for an app publisher to delete reviews. However, in the Google Play Console, as an app publisher you can flag comments as against the Google ToS, about 100 per day maximum and then the reviews go through moderation at Google. Here, it's more like a bulk deletion was done (certainly manual action) and I doubt it's just one single moderator taking action to delete 100k+ reviews.