@John ******
the DTV is indeed nothing more than a glorified tourist visa. And I don’t think it would qualify as ‘residence’ per se. But maybe!
But that is a different issue. You are asking whether or not a third party national can apply for Schengen visa from within Thailand, which is a good question. My partner did so last year and received her Schengen visa from France. But I understand it can be an issue.