Anything perish in the tank? Something as seemingly insignificant as a snail can cause an outbreak in a smaller tank - you didn't mention if your tank was 2 gallons or 200 gallons.
Going a week without dosing vodka woudn't have contibuted - mainly because you'd only been doing it for 2 weeks prior to leaving so the dosage should have still been minimal.
I would lean towards decaying specimen or overfeeding in your absence. Also possible that the algae made a comeback on its own and it just happened to be while you were out of town - you mentioned that you already had some hair algae but it was mostly gone.
Pull what you can, scrub rocks with toothbrush and siphon, minimize feeding, blackout the tank (reefs can go 3-5 days) and do water changes.
Here's an interesting overview of various algaes.