"Recent Items" show files that I have not recently opened

Question

I use Outlook for work, and when I go to insert an attachment, majority of the time the files that show up in "Recent Items" are items that I have not recently opened. In fact, the document that I was just working on and saved will be 3rd or 4th down on the list. However, the files that are 1st or 2nd tend to be personal files like my drivers license or tax docs..., which I haven't opened in days if not months.
My Microsoft Account is my personal account, and no one else has access to it.
Does this mean an unauthorized person has hacked into my Microsoft account? And if so, how do I get them out?