Quote from stefan_777:
He said he was only short CDN, long USD. If it's true that this was the only FX position he had, it doesn't explain why he was liquidated. CDN fell against USD, which rose that day.
But when IB says he had a non base currency position that was losing substantially, then there has to be something other than the short CDN/USD. Because aren't those base currencies for IB?
USDCAD dropped from 1.074x to 1.050x from 2:30 to 3:30 EDT. That's >2% there. He may have gone short loonie as shares dropped, and it reversed, but the USDCAD was never down by 3.6% on the day.