It isnt that they dont care about the subject, its that you care enough about the person that you try to understand why they like the subject.

Some people interpret this to mean you have to fake interest in the subject, or you have to be honest that you don’t like said subject but it can also mean you take interest in the subject simply because the subject is of interest to the person you’d like to be friends with.

Again, this a bit of a skill and takes practice