I just checked the account in the official history and would like to add that the landing on the main beach was between 0520 and 0525, or about 30 minutes after the start of nautical twilight. (The times were expressed in British Summer Time, which was an hour ahead of GMT.) Furthermore, Dieppe lies in a basin, so the sun probably may not have appeared and almost certainly could not have lit up the windows.
There were attacks by Hurricanes on the town prior to the landing, but these were strafing, so large fires should not have been set and would not have time to spread in the stone buildings around the harbour. There were no heavy bomber attacks on Dieppe itself during the night.