I play guitar, I play guitar hero, It's a big difference.
Some people join the army and play shooters, it's a big difference.
People who say that are just arrogant assholes who think that they're better than someone else for playing mainstream metal on their over the top guitars. Guitar hero is a party game that is fun to play when you're bored while Guitar is a serious instrument which takes time to master, but it hugely satisfying to play. I can't play a lot of the songs on guitar hero, and I either don't want to or can't be bothered to spend weeks learning and perfecting it when I could spend 15 minutes playing it on a plastic controller where I can feel like a king