my theory is hashnest manipulated market.
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This actually has a lot of merit and grounds looking back at the charts at the hash-rate and diff it now stands out that indeed there must of been machines with higher TH rating (s11) hitting the network back then the spike in diff was for me not a linear move it was very much parabolic in nature.
If this is the case and users of hash-nest have been basically scammed and this can be proved this is really going to end badly for them though saying that seems to me if your in china you can do what every the hell you want.
I do see the similarity as you said phill regarding the Bunker Hunt Brothers and there attempting to corner the market in silver we all know how that ended up.
That I think is what Bitmain did (push up the diff & corner the market) Only I think there plan might just have backfired on them in a big way.