It isn't simple. The judgement states that broad implied deference to the agency of the act in question, per Chevron, is incorrect and the courts decide in the those case.

There were a ton of arguments that interpretation, in general, is an Article 3 right of the courts. Though, I'd assume if congress explicitly granted interpretation to the specific agency of the act, we'd have a separate case on whether they're allowed to do that (explicitly defer).