The author definitely seems to want to modify the adverb, but "distractedly quickly" is semantically still nonsense even if you use "ly" instead of the ungramma

The author definitely seems to want to modify the adverb, but "distractedly quickly" is semantically still nonsense even if you use "ly" instead of the ungrammatical "ily". "Distractingly quickly" would be meaningful though ("I was distracted by how quickly he ate the mango"). I wonder if the author is just trolling here.