Could be a coincidence. Maybe every time you drove by, it was mid off-cycle, and then this time it happened to be on. I suppose an intermittently working ignitor could be the cause, but IDK if that is likely. Some lamps take really long to cycle, I have seen one that takes around a half hour to cycle off.
Or maybe it is some sort of other intermittent connection, that is possible.
I feel like I just ate a jaw breaker from the TV show Ed, Edd, n Eddy.