It depends how you define hero. Just because someone has a superpower doesn't mean he will act heroicly. Therefore there could be several people introduced with super powers, but not all of them will be heroes.

I believe that preview was for Episode 7 which introduced two more heroes, Micah (technopath) and Ted (nuclear fusion control).

This episode introduced a few more as well, Eden (brainwasher?) and Charlie (memory/learning). The other questionables are the kid in Mohinder's dreams and Mohinder himself. Of course, we don't know if the kid in his dreams is alive. His sister was also revealed as being "special".

You could also say that Eden was not discovered in this episode (which she wasn't - only that she probably has a power).

Either Eden, the waitress, or the kid: one of them doesn't have powers.

I say this because for the preview of Episode 8, they said "2 new heroes will be discovered"

If you can't count, that is 3. So I assume one of them has been incorrectly labelled as a hero by us...I say Eden. Powers of Persuasion isn't really a power...

I got the impression she could control people's actions.