Possible Identity Theft??

My husband has been attempting to get a credit card or two to help rebuild his credit score, and recently we had something strange happen when he was applying for a card at a store.
When he got to the part of the application process where the associate put him on the phone with someone who I assume was from the bank/lending part of the company, she asked him a couple of questions including security questions. The strange part was that two of the questions were referencing a woman whose name he did not recognize. We realized after he got off the phone that the only person we knew with the first name was his brother's wife, and with a quick phone call to his mother we learned that the name being referenced was in fact his sister in law's maiden name. We checked his credit report and nothing strange was noted, and we even checked with the company to make sure there was not already an account open with them attached to his SSN. It seems as if nothing is wrong, but we are very concerned about the fact that his sister in law's name would come up in a discussion about his credit in any way, shape, or form. No one can seem to answer our question about whether we should be concerned and what we should do about it just in case, and I was hoping someone here might have some advice. As a side note, the main thing we are concerned about is that perhaps they somehow forged his identity to co-sign on a car loan they got sometime in the past year; wouldn't that show up on his credit report, though?
Thank you in advance.

 

That is part of the concern, actually, and I guess I should have mentioned it. We have reason to not trust his brother because of past actions. My husband has not talked to his brother in a couple of months, by choice, and we want to be careful about starting an accusation war until we have proof of reason to be upset. We know the car was purchased when they were living in another state, but we do not know the dealership it was bought from.