Some fish just jump just for the hell of it. If you ever stand by a body of water long enough you will see that. Arowannas, trout and others jump when they hunt in nature, carp do it when they breed, and some just jump. I lost a giant danio to jumping once. i am sorry to say, but I was happy to be rid of him.
I would get a cover, silver dollars are strong swimmers and I would be scared. I feel for your loss.