How did flipper get property lower than market?

So i have my eye on a property listed by HUD for $235000. It's out of my price range for the house so i keep waiting and watching it for month. The price never change until suddenly the house was sold. I checked the property appraisal for the sell price and it was $172,700, even lower than the county appraisal value of $206,607. It's in a super hot zip code, and I don't understand how a flipping company can get it at that price.