Well, it depends on who you mean by "they" here. If you mean Slate writers, then actually no. I got it straight from their article (admittedly, Slate-anything sure is a mess to dig through). They make it clear they made their own survey later on and the data advanta regurgitated here came from that one. There isn't even a single reference towards political views of the participants in regards to the first study made by GfK, which is covered rather early in the article, so that should have already been a red flag.
Now, that's not to say Slate isn't without fault, the entire second paragraph, as well as the last bit about lack of disclosure (speaking of which, the lack of disclosure about the second survey kinda inhibits anyone willing to dig further than I did from getting anything tangible) in the first paragraph was about what they did wrong. But at least, unlike advanta, they didn't try to prop that 52% number by running GfK's name through the mud. But if by "they" you're referring to advanta, then yes.