Could be normal variance. Or could be really the Chinese ban... Time will tell. But I will laugh oh so hard if it is the second one because the BTC chain won't be able to survive it while the BCH one can because of the new DAA.
You have it backwards, hashrate is the hashes per second that attempt to solve the equations to find the next block. In other words hashrate is essentially the output of all mining machines attempting to find the next block. Difficulty is the difficulty of said equations, which has been steadily rising over the last few adjustments, and adjustments are made ~ every two weeks. So a sudden loss of hashrate is likely to result in it taking longer to find the next block. Basically, difficulty is based off of block times, which can be based off of hashrate. How I just explained it is definitely an over simplification, but thats the idea, it's actually possible that the difficulty can stay the same and the hashrate can drop and blocks could still be found minutes apart, its just very unlikely that that will be the case.
> Difficulty is the difficulty of said equations
The equation doesn't change though, it's how difficult a block is to mine that gets accepted. (how many leading zeros, the more zeros the higher the difficulty)
How would you determine the hashrate? Sounds to me like it sould be something like
* how difficult a block actually was (how many hashes it should take to get a similar difficulty block)
* compared to how difficult it should be (the difficulty)
* and how long it took to actually mine it (the difficulty target)
Am I wrong?