I understood what he meant. The nitrogen is "made" during the same process that isolates (makes) oxygen from air.
I like the tutorial on the aristocratic (OCP?) gases.
It's actually the other way around. Oxygen is 'made' during the process to isolate N2 from air. N2 is more important, economically, then O2. And, if you make liquid N2, O2 will condense in it. We don't leave open vessels of N2 about for that reason. You can concentrate O2 in it and go Boomba! Boomba!