What does it mean when you're added as an authorized user to a stranger's credit card?

I checked my credit report and I am an authorized user on someone'a credit card. It has been active for a few years and is in good standing.

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I called the credit card (Chase) but they couldn't locate it or remove me because the credit report didn't show their name or full account number.

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I have contactes 2/3 of the credit report bureaus explaining the situation. It only appeared on 2 of them.

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I just want to know if this is a really weird scam or somehow a case of identity theft or something else that needs further action.