Is it possible to accidentally ejaculate from getting scared?

We are both home from college. We were having sex in his basement and suddenly the light for the stairs turned on (his family members always turn it on before they come down at night) and immediately my boyfriend saw it, stood up, and went to grab his clothes. He told me to go to the bathroom and stay there, becuse if anyone came down he could just tell them I had to use it. It ended up being nothing...no one came down. So we kept going.

Is it possible that he got so scared in that moment that he came? I'm only asking because when we have sex I always know when he finishes...but this time I'm almost positive he didn't come, even though he said he did. He told me he came on my *** and I didn't see anything nor feel anything.