Montag walks Clarisse home and sees the lights on. What does he think is strange?

Montag doesn't see the lights themselves as strange, but is shocked by the number of lights turned on in the house. His first reaction is to ask Clarisse what's going on.... only to be further shocked to hear that her parents and uncle are simply sitting around conversing.

"What's going on?" Montag had rarely seen that many house lights.

"Oh, just my mother and father and uncle sitting around, talking.