according to main stream interpretations false prophet is not talking about the devil. we know this because Revelations talks about the devil himself possessing the anti-Christ about midway through the tribulation and having a false prophet. the devil cannot be in two places at the same time. only god is omnipresent.

pureevil... a "prophet" might not know what you had for lunch or dinner because they are NOT omnipotent (all-knowing), they simply have a gift of precognition that is only limitedly under their control. it doesnt mean they know all, just certain things...