The fact that they were mentioned once is enough. The keys were an integral part of the story, or do you think Christ uses symbolic language for superfluous reasons? There is no "secret teaching", we're not gnostic, and evolution is not a dogma so no one is required to believe it at all.
The fact remains that the story is told 3 times. Each time it is told, the recurring theme is belief in Jesus.
Story 1: Jesus is the Christ!
Story 2: Jesus is the Christ!
Story 3: Jesus is the Christ! PS - Peter is in charge and beleiving this is a condition of salvation!
Don't you see the absurdity of your claim.