Why does "My Documents" on old Windows 7 install drive letter X: point to "My Documents" on C:

Question

I'm throwing away an old computer and removed the drive from it to repurpose it. I have some saved data in My Documents. When I mounted the drive onto my main computer, surprise, the My Documents folder now points to the folder on C: drive (C:\Users\MYUSER\Documents) instead of opening it on X: where I have assigned the old drive.

X:\Users\MYUSER\Documents is almost empty, just the default stuff (music, pictures, videos, all empty). X:\Users\MYUSER\My Documents, which is a link, points to my C:\Users\MYUSER\Documents.

Maybe this confusion is generated by the fact that my username is the same. To try to work around it, I renamed the Users folder to UsersA and my username too. It didn't help. The X:\User\Documents folder is empty.

As this is an old Windows 7, I'm quite sure I didn't encrypt my home folder, not even sure if it was possible in this version of Windows :D.

Do you think that simply by mounting this drive on another computer Windows wiped some information located on the other drive? Kind of doubt it, since I didn't do any writing on that drive.

I also tried using an "undelete" software to try and dig in the file system. It's empty there as well. And I'm absolutely sure this shouldn't be so. I had stuff there.