Derogatory credit remark appears on spouse's report?

I have a small (under $1,000) really old debt, about half a decade old. Totally forgot about it until recently, only noticed it again because it has suddenly appeared under my WIFE’S credit report.

Is that right? The card was opened by me, I never added her to it, and it was opened and closed many years ago, definitely before we got married. Also the date on the debt is suddenly July 2015.

I thought that credit reports didn’t merge?