If you mean "some apps have ads in them," that is true. What I mean is the OS doesn't have ads, unlike Google and Amazon's competing products... And unfortunately even Roku now.

You are free to never open apps that have ads in them on the Apple TV.

(If you mean: installed apps are allowed to show content previews when you hover on them in the UI — I think that's pretty different from an ad, and it's a feature I personally like, since it means I can easily resume a show I was previously watching without even having to open the app-specific UI. That's quite different from my perspective than showing ads for services and apps that I've never used, that I can't remove.)