Thou art Simon the son of Jona: thou shalt be called Cephas, which is interpreted Peter (Petros.
Yes it does mean rock. Petros means a small rock or stone. On the other hand, petra, which Christ said the ekklesia would be built on is an unmovable rock.
4073 (pétra) is a "solid or native rock, rising up through the earth" (Souter) – a huge mass of rock (a boulder), such as a projecting cliff. [http://biblehub.com/greek/4073.htm]
4074 (Pétros) which is "a detached stone or boulder" [http://biblehub.com/greek/4073.htm]
So I agree with you. Someone's interpretation is wrong. Peter indeed was call a "detached stone or boulder". Something movable. But Jesus said He would build His ekklesia on an unmovable "huge mass of rock". Would you rather be part of an ekklesia build on a moveable "detached stone" or an unmovable "huge mass of rock"? I think the Holy Spirit chose the words He used for a reason.
And it isn't Peter.
Also, here, Paul identifies who petra is, and that is Christ. This link takes you to the Greek.
http://biblehub.com/text/1_corinthians/10-4.htm
1 Corinthians 10:1-4 For I do not want you to be unaware, brothers, that our fathers were all under the cloud, and all passed through the sea, and all were baptized into Moses in the cloud and in the sea, and all ate the same spiritual food, and all drank the same spiritual drink. For they drank from the spiritual Rock (petra) that followed them, and the Rock (petra) was Christ.
It simply cannot get any plainer.
....the Rock (petra) was Christ.