Not surprising at all. Ad buyers have an immense amount of control over how much is spent and targeting, and with all the user-provided information Facebook can seriously drill down and find an audience for any campaign.
From the link:
Chances are that at least one or two will be targeted to the activities and interests you post on Facebook, or the city you live in, your gender, or even your relationship status. These little ads are typically purchased through Facebook’s “self service” system, which enables small- and big-time advertisers to create an ad in minutes to lure specific demographic groups with a few lines of text and a graphic or photo.
Rather suddenly, these little come-ons have turned into the leading source of Facebook’s revenue. My estimates, as an analyst at eMarketer, the New York-based market research firm, show that self-service ads account for at least half of Facebook’s total ad revenue, projected to be $1.3 billion this year. That’s way more business than anyone could have expected, given that there are no upfront charges to placing these ads and that Facebook only earns revenue when viewers click on them or when a certain threshold of impressions is reached.