They are calling and using credit agencies' databases to verify your identity. What is interesting is that TSA's authority only extends at the checkpoint to search passengers for weapons, explosives and incendiaries. The regulations have never been changed to require confirming identity as a requirement to clear the checkpoint. In fact, in the Gilmore case, the TSA stated that the alternative to presenting id was a more thorough search of your person and possessions, not that you would be unable to be cleared.