TL;DR: Interstellar hydrogen clouds could act like a naturally occurring galactic maser (a mechanism to amplify microwaves like a laser amplifies light), emitting a beam of intense microwave radiation when zapped by a flare from a passing magnetar (a neutron star with a very strong magnetic field).
Whether it was or not, the article is talking about two scientists who see emissions similar to the WOW signal all the time just with far less intensity than the signal. They made the connection and extrapolated how it might be possible to see something like the signal.