Anhedonia can have many causes. Hate to say it but there is a spectrum of people who are less emotional to those who are extremely emotional. It is hard to say where either end turns pathological, sometimes it is just that person's normal.

Anhedonia can exist on its own or following things like dysthymia, schizoid or what was in the past called schizophrenia simplex. Or following antidepressant treatment.

It seems that the reward system in the brain is not as active. Of course that can happen for many reasons.

I knew a person like this, friend of a friend. He was nice and all, but I felt he lacked something I had. It felt like somewhat of a mystery to me, but then again people have claimed I'm a mystery to them so... yea, LOL.