Linoleum Floor Water Damage
The discoloration you see on the linoleum floor this from
water that is getting underneath the flooring. Instead of removing the
toilet when the linoleum floor was installed, they simply went around it
and then applied the necessary caulking at the base of the toilet.
If that caulking separates at the base of the toilet, this will allow moisture to work its way into the linoleum flooring and over time will cause the flooring to stain.
If you look closely at the base of the toilet, you can
see the linoleum flooring starting to curl up and separate from the
caulking and the toilet.
Nothing can be done to remove the stain from the linoleum and the flooring will eventually need to be replaced. It's always better to remove the toilet when installing linoleum flooring or tiles and your bathroom.
Behind the toilet there is a gap where the linoleum wrap around the toilet. If the toilet was removed during installation of the flooring, this gap wouldn't be there. This gap also allows moisture to work its way underneath the linoleum flooring.
The gap behind the toilet is your first clue, that the toilet wasn't removed during the floor installation.