More likely these were registered by cranks of some kind. Let's keep in mind that the World Trade Center is such an obvious choice as a target that it is not really surprising to see such a scenario discussed prior to the events of last week.
I suppose also that people connected with certain groups may have tried to warn people in their own way. This is one area where we'll just have to let the FBI investigate and interview the person who charged the registration to their credit card. In the meantime, I don't think we should read any more into this than the evidence dictates.