I think he meant that if mars had the same atmosphere in mass as in earth the pressure would be only 0.38bar. But if it had a more massive atmosphere there, pressure could rise more.
I fell too that this master-slave thing is a overstretch and a little hysteria. That being said, I do think 'main' is a better name for what this branch is supposed to be and it might be better for beginners to understand. Of course, 'master' is the term we are all used to and that will cause a lot of confusion and broken pipelines too.