Since "rock" is a metaphor ... unless I missed the part of the New Testament where Medusa showed up ... I don't see why it should be a surprise that it was used in more than one context. Jesus referred to Peter as "the rock"; Peter and Paul, in their letters both referred to Christ as "the rock."
What's the problem? Different context, different intention.
Is this the mark of a genuine movement or is this the mark of a movement that is defined as the "un-___ fill-in-the-blank ___" movement?
Please note the caveat, again, that I am not attempting to lump ALL protestants in this group...but there are a small but VERY noisy subset who, for some reason, must question their own salvation if they are not condemning others to hell each day.
This type of thing was foreshadowed by both St. Paul and St. Peter, as documented in scripture, e.g.: In them there are some things hard to understand that the ignorant and unstable distort to their own destruction, just as they do the other scriptures.