I thought maybe I was using the phrase wrong, but the first two definitions I find are "the internal sense of being good enough and worthy of love and belonging from others" and "a feeling that you are a good person who deserves to be treated with respect". You'll note that those are both inherently social. And both "good enough" and "with respect" are about one's position in the caste/hierarchy structure.

The reason I assume what the psychologist meant is that most of them are neurotypical, and neurotypical people are deeply invested in social primate dynamics. I understand that this is hard for neurotypical people to see, but you might read things like DeWaal's "Chimpanzee Politics" or Johnson's "Impro" [1]. Plus there's my personal experience, where psychologists are very inclined to talk about self-worth in the social sense. And I think that's fine; I'm sure it works well for their neurotypical patients.

[1] particularly the section on status transactions, which are vital for authentic theater performances, but are rarely articulated because it's so natural to neurotypical people

I think what they simply meant is that neurotypical people are a lot busy with making models of hierarchies between people and finding out their own position within that hierarchy, and mostly automatically or unconsciously derive self worth from that.

While some types of non neurotypical people don't automatically spend their mental energy on such thoughts and analysis. That is maybe why 'self worth' feels a strange term to them. They simply are who they are and will not try to come across as this or that type of person (helping, smart, empathetic, strong character etc) . Neurotypical people hence find the way they come across weird.