Spike isn't particularly surprised by the show of power, but it does put him a little more on alert about the possibility of this guy being more insidious than harmless. He's got powers- in Spike's book, that usually means demon or witch, and he doesn't look like a witch.

"I assume you're coming." Unless he plans on locking Spike in or he's just bored, he can't suss out any other good reason that he might open up the window. He takes a quick glimpse into the room and then slides in, landing feet-first onto an old tanker desk. The room itself seems like it contains mostly old files or maybe records. Paperwork of some kind. It's also dark, but the light from the window is enough for Spike to see by.

He hops down and turns back, pry bar in hand. The room isn't really what Spike had been looking for, but it's a good start. He recognizes similarities from the last time he'd been down here back in his universe.