In addition to a sibling comment about median, it could be that or that other common method (I forget, bayesion average? I think), but also consider - 176K revi

In addition to a sibling comment about median, it could be that or that other common method (I forget, bayesion average? I think), but also consider - 176K reviews, 76 days since the _expose_, if it were 100 reviews a day on average, that's still 7.6K reviews. If it were 10K in the first few days, then 7.6K after, it's still ~10% of total reviews, where they likely had a ~4.6-8 score before hand. A drop in the bucket. And it's possible (though imo unlikely) that some reviews were removed, perhaps initially at least, due to suspected botting.