Ben almost points out the circumstances of his hearing of the Mysticalman, but catches himself just in time, because that would risk exposing his secret identity, wouldn't it?

Instead, he just replies, "You are?" He doesn't sound quite as incredulous as he maybe should, but he is sort of bewildered. He would think that he would have heard of this guy more in that case. He also doesn't question the bit about the journalists, because even if that were true, Ben wouldn't know it because newspapers are boring and he doesn't read them.

But the fact is, whether or not any of this is accurate - again, Ben needs to be making some connections here. "...hey, if you want to team up sometime, that could be cool!"