[ In this passage, Christ doesn't say "the" -- he says "this very" - the word tauth -transliterated taute - you may recognize it from our word tautology. It means "the same". It's intensified with the demonstrative pronoun th , so it's not just "this rock" - it's "this very same rock right here". Don't see how he could be much more emphatic than that. It just isn't possible that he meant "a" rock. ]
Not at all if you "get" the metaphor.. If you do not get it, the metaphor can mean a number of things.. Thats usually why a metaphore IS used, to make a partivular point.. Not to forget he was talking about a meeting place made of many rocks.. while he was saying the very metaphor to THAT rock..
Certainly Caesarea Phillipi has a lot of rocks lying around, but Christ wasn't talking to them ('tell these stones to become bread') He was speaking directly ('thou') to St. Peter.
Christ used quite different language when he was speaking in metaphors - as in the parables.