In addition to new SHA256 miners joining the fray, these miners are also probably jumping back and forth between BTC and BCH, depending on what is currently more profitable.
Now that BCH is going up again, I wouldn't be surprised if the next difficulty change would be negative.
That may very well be the case, however I would like it if they left bitcoincash permanently. Bitcoin cash did bounce up again but if you look at the bigger picture things aren't looking great. Difficulty is directly related to the amount of hashingpower in the network so I hope miners are dedicating more hashing power to the main (lagacy) chain rather than mining bitcoin cash.