Most large farms run auto switching pools now, if BCH is more popular, the whole farm is mining it, when profitability drops, people cut back.
exactly this. and any extended hot streak ie 30 blocks in 2 hours vs 5 hours can alter hash rates
or cold streak 1 block in 2 hours .
or better yet 1 block in 2 hours followed by 30 blocks in 2 hours will make a spike.