Of course, it's possible Scotty simply hadn't gotten around to checking his messages yet. He was asleep in his lab when they found him, and by the looks of the place, he spent his time tinkering with and dismantling things rather than listening in on galactic chatter.
But it's not galactic chatter - it's an emergency distress beacon. It stretches credibility further when you consider how long Kirk's been on the planet when he arrives at the outpost.
This is something that does chime in with the comics too. NuScotty is a fantastic engineer but he's a terrible, terrible officer. Star Trek always seems to think your best engineer should be in charge even though chief engineers spend a large chunk of their time supervising underlings and dealing with admin. Your talented engineers can be your petty officers and specialist technicians. Officers need to know how to follow protocols, including quarantine and emergency protocols. In the same way that I thought Kirk should have been promoted to work under a more experienced captain before taking command of a ship, all the evidence I've seen so far is that somebody else should be in charge of engineering! Scotty may be a genius but he's also a dumb a**.