The scope of the warrant has to be spelled out on its face. The police can't rely on an illlegal search to justify obtaining a warrant. That's the fruit of the poisonous tree. It's called cheating.
If the police saw a pot plant in plain view, that is from a position where anyone could see it, that may be sufficient to obtain a warrant to search the house to see if a large grow was underway. What else was found?
I do not practice in NC, but I may offer some general advice. I agree with the first answer, in that the search warrant must spell out where to search and what the police are looking for on its face. As soon as the police realized the plant was fake, there was no longer probable cause for the search warrant, and the search should have ended.
If the police found something illegal and you or your boyfriend are being charged criminally, you need to consult with a local, experienced criminal defense attorney immediately. You may have a valid motion to suppress any evidence found during the search.
Good luck to the both of you!