The thing is many people don't even know what heavy metal is.  People say metal is Korn but it isn't... heavy metal for one is not Godsmack so yeah it's an opinion but there's a lot of basis for that.  Comparing a heavy metal band and Godsmack can show that Godsmack MAY HAVE heavy metal influences but their grunge roots show more from bands like Alice in Chains and also their hard rock roots (their last full length, "Faceless" definitely has shown their hard rock influences.)  But honestly, heavy metal should be taken out because, in a simple example comparison, Godsmack have more to do with bands like Staind than a band like, say maybe Judas Priest or Iron Maiden or Dio, all which are heavy metal. 

 Next, about the NIN issue, well to my knowledge, I remember that there was some controversy behind that with Trent and NIN fans against Godsmack but it wasn't any huge music news but I'll search into it more and reveal what I find.