I don't see anything in my comment implying "Fly" to be either keyword or Ability (if we're using the new terminology).
I'd agree with the Tau having an army wide rule that lets 'Fly models' do certain things.
"And all the fire-caste say; I'm pretty fly for a Mon'Keigh!"
This world exists because of the things we have done, forever branching to the decisions we make and twisting to what we do not.
”Woe to our enemies. We'll tear them apart regardless.” ~Barrywise