...social advertising is so new that nobody knows for sure [if it improves sales]. It's still unproven, untested and largely unstudied.
This simply does not follow from the anecdote of one tiny campaign, so it's coming from somewhere else.
I don't want to ascribe malicious intent to the authors, so let's rebute their conclusion directly: "social advertising" isn't wholly unlike other forms of advertising, with the principal difference being that you now have access to a lot more data when deciding who sees your ads, such as people's declared preferences and their social network.
It's up to businesses to figure out a media strategy making use of those data. Sure, this might take time/experimentation, but also seems quite obviously a better deal than placing ads in the Yellow Pages or broadcasting them (nearly) indiscriminately on TV or radio.