The author did not need to define schizoid because:
1. It is their blog, and they probably assume their audience is educated in what schizoid means or is capable of looking it up.
2. Schizoid does not colloquially refer to schizophrenia, and schizophrenia is not a pejorative for "crazy," these are both real and distinct (but related) disorders that do not require anyone talking about them to dichotomize them from what you might assume people misconstrue their false definitions as.
Also, it's not an "extreme form of introversion" - it's much more than that, and putting it that way minimizes the serious nature of the disorder.
You're incorrect on point 2. In many communities, schizoid/schizo does refer in a derogatory/shorthand manner to schizophrenia and many more people are familiar with schizophrenia than schizoid disorder, so that is more likely to be the immediate assumption.
> 2. Schizoid does not colloquially refer to schizophrenia
It often does colloquially refer to schizophrenia, I've heard people use the word this way for as long as I can remember. General purpose English dictionaries document this colloquial meaning, I checked several to be sure:
1. It is their blog, and they probably assume their audience is educated in what schizoid means or is capable of looking it up.
2. Schizoid does not colloquially refer to schizophrenia, and schizophrenia is not a pejorative for "crazy," these are both real and distinct (but related) disorders that do not require anyone talking about them to dichotomize them from what you might assume people misconstrue their false definitions as.
Also, it's not an "extreme form of introversion" - it's much more than that, and putting it that way minimizes the serious nature of the disorder.