How does the xdg-open command know which application to use to open a file?

I would expect xdg-open command to use the same application that opens when I double-click the file in the default file manager, but this is not always true. For example my DE is XFCE, my file manager is Thunar and my default picture viewer is Ristretto. However, xdg-open example.png opens the example PNG file in Pinta. Why?