Dropping the light doesn't instantly drop their aggro completely. The monsters will run to the last place they saw the light and conduct a search before returning to their patrol. If you are in their path, they can still find you. They aren't completely blind in the dark, but their perception is greatly reduced, that perception goes up slightly if they are in search mode as well.
Thanks for playing!
Sorry if you read this twice, I accidentally posted it in the wrong spot and moved it here.