He does cheat to get rebounds. Unless you are a guy like Doncic that plays PG on offense and forward on defense, if you are getting around 10 rebounds per game, you are hunting for them, grabing rebounds that your teammates could have had. It isn't that big of a deal (proving that you are not leaving your guy open to go after rebounds), but it isn't a difference maker for your team either. The rebounds that make a difference are those contested ones. The type of rebounds that bigmen get.
And relax, I'm not taking anything away from Murray. There's nothing I'd like more than for him to become a mega-super-duper star. I'm just stating something that I think should be pretty obvious for NBA and Spurs fans now: guards grabbing rebounds isn't a difference maker, and Murray needs to work on that offensive efficiency. I don't see how that's hating on the guy.
Also, yeah, if you are ever serious about winning, being Westbrook-lite isn't ideal.