If you can get involved enough with the character in the game then it can be role-playing, and then I added an 'or' if you can effect the story through choices you make.
You can't effect the story in most RPG's, they are just scripted stories in which you're along for the ride. In a lot of them you're given choices to make, but often these are superficial and don't effect the story out come.
And yes thief 3 is also a first person sneaker, in the same way that Beyond Divinity is a 'cabinet' view action collect-em-up! Both with their own character elements and story.
