It's a reference to the famed Ayn Rand novel "Atlas Shrugged," in which protagonist John Galt leads the entrepreneurial class to cease productive activities in order to starve the government of revenue....
I agree with Hilzoy about the reference. He says it's strange that the producing entrepreneurs seem to be staying in place.
Much more obvious is that it is not the Randian Ubermensch that are dropping out: it is the workers/consumers. They've closed their pocketbooks and ceased spending as much, starving the entrepreneurs who now have unaffordable overhead on their idle productive capacity.
The interesting thing is that Rand had wrong in so many ways if you want to consider this analogous to "Atlas Shrugged". The causes were a real estate bubble and interlocking dependencies between banks. The players are essentially all from publicly owned corporations, rather than privately held corporations led by the owners. I haven't read Rand in 35 years (who could stand it as an adult?), but I don't think she mentions bubbles or bankers or non-owners as causing the collapse.
So if anybody is using the term "Going Galt", they're WAY OFF, and probably trying to pretend they're powerful in this crisis, rather than helpless. They'd like our supplication, not our scorn.