RE: Why does my paint match?
It was certainly more atomized with the airbrush. That alone will cause a different sheen.
Also, It may have been mixed a little more or less than the first bach.
It shouldn't matter anyway, I have never been able to touch up without having to wet sand and polish for a glossy fininsh.
Or, scuff with scotchbrite and/or wet sand a flat finish.
Doug