Furthermore, why did he get stopped out at the open instead of the close on friday ?
Thanks Athena for your contribution,
Just my own explanation for this question is that at friday close, my two trades EURJPY (short) and USDJPY (long) were in kind of hedge and my total margin was larger than the limit of stop out. In Monday open, with real market prices, my margin should have been even larger than friday close because of larger drop in EURJPY with respect to USDJPY. But, what they considered is that, not even at market open, but after 24 seconds of market open, they considered the new price of USDJPY which was against my price but friday close price of EURJPY (which was 300 pips larger than the real market price in that moment which would have been in my favor if they would considered it correctely). Because of this 300 pips which they didn't consider in my favor for EURJPY, my acount got the stopped out call.