That would explain the (pretty significant) volume drop on Huobi, but why BTCe, Bitstamp, and Gox?
Because those are Chinese traders too.
BTCe is Russian, and Gox is based in the United States, not sure about bitstamp
BTC-e is based in Bulgaria, not Russia. Both BTC-e and Bitstamp, based in Slovenia, are European exchanges. MtGox is based in Japan.