Why are you surprised that his stop order triggered? I can imagine that if it is set to monitor bid prices, and the bid price drops to below $35.00, his stop loss order got triggered. And in this case apparently got filled at $35.00 as well.
If my broker triggered a stop just because the best bid was at my sell stop price, then I would either never use stops at that broker again or pull my money immediately. That is not how stops should be handled. The OP should investigate why the order even triggered as there was no evidence in my time and sales that it should have triggered. Of course, my data could be incorrect.