Your card very well could have shown up in the PokerStars system as "flagged". In the banking world a "flagged" card is one that has been linked to a database that has been compromised by a hacker or group of hackers.
All of your information....(card number, issue date, exp. date) is stored in a huge computer with every other member of your bank or credit card company. Sometimes hackers take a shot at these data banks, and are able to break through security. Companies/banks will often issue new cards to members because of happenings. 99.9% of the time it means nothing, it's just a safety measure. It's happend to almost everyone I know at some point in time.
The last thing you should worry about is PS trying to steal your identity. With the number of players that pass through the software daily, and the amount of cash that circulates through the company, I am sure something just popped up on your card account that came across as funny. If you don't want to give them ID, don't. But when you registered your account you agreed to verify your identification if PS ever asked you to, with the freezing of your account being possible punishment if you refused to oblige. I really don't think it's a big deal, I've had to send them ID twice.