It seems that Paul understood that Christ was referring to himself as the rock. Makes perfect sense too considering other passages such as Matthew 7:
24 “Anyone who listens to my teaching and follows it is wise, like a person who builds a house on solid rock. 25 Though the rain comes in torrents and the floodwaters rise and the winds beat against that house, it won’t collapse because it is built on bedrock. 26 But anyone who hears my teaching and doesn’t obey it is foolish, like a person who builds a house on sand. 27 When the rains and floods come and the winds beat against that house, it will collapse with a mighty crash.”
If we build our foundation on Christ, the rock, we'll be solid. IF we build our foundation upon any man...even Peter...we're building on shifting sand.
Greek and Aramaic translations, please. Thank you.