The theft is Bitfinex's liability.
So all non-BTC accounts on Bitfinex should be affected proportionally. I presume Bitfinex will eventually realize this. Unless law is somehow different in Hong Kong.
I presume the knee-jerk selloff of BTC is an overreaction. Bitfinex still has significant resources, so everyone on Bitfinex should probably get a loss but not a total loss.
Joel Katz is mistaken:
In other words, the pertinent qualifier is, “segregated from what?”. The crypto assets were segregated at least from the other business liabilities of Bitfinex, but not from each other (or at least not BTC accounts segregated from each other).