It's not a mistake in their copy, which is unambiguous, it's just your incorrect reading of the antecedent.

The headphones themselves are always referred to in the copy AirPods Max, never as "a device".

The headphones are unusable without a source, referred to in every single place in as "a device".

I get making the mistake, but there's no need to double down when someone points out you've misread.