How the Fifth Sea Lord related to naval aviation

Was the Fifth Sea Lord also the Royal Navy's Chief of the Naval Air Service?

Effectively yes; the two functions were combined in the Fifth Sea Lord's office.

The Fifth Sea Lord and Chief of the Naval Air Service functions were effectively combined, much as the First Sea Lord also served as Chief of the Naval Staff. Alexander Ramsay's Fifth Sea Lord appointment therefore carried responsibility for naval aviation. A Sea Lord title could bundle a broad policy portfolio rather than denote a single shipboard command. The office placed naval air policy inside the Admiralty's senior leadership structure.