Here is the same statement said to all the disciples without reference to the "keys", verse 18. Therefore, this statement can and does stand alone as a separate thought not necessarily in regard to the "keys". I submit that when Christ said this he was not referring to Peter alone but all the disciples. Verse 19 below further describes this binding and loosing as anything two disciples agree on.
Matthew 18 1 At the same time came the disciples unto Jesus, saying, Who is the greatest in the kingdom of heaven?
18 Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven.
19 Again I say unto you, That if two of you shall agree on earth as touching any thing that they shall ask, it shall be done for them of my Father which is in heaven.