Their orders ledgers on GRIN looks healthy, but their trade history is most likely fake (the smallest traded amount is about 150 GRIN and the average is about 400 GRIN per one trade).
If for example you check Bittrex (https://international.bittrex.com/Market/Index?MarketName=BTC-GRIN) you'll notice many small trades of 2-5 GRIN, those could be miners selling or trading other mined coins for GRIN.

If HotBit is faking their volumes, I wouldn't want to support them just because of that.