I think his choice of Octave was really just to avoid using Matlab. I had taken several other courses around the same time, and they all used Matlab. All of the courses had arranged for a free Matlab license for the time the course was active. You also were given the option of buying the Student version for $99. That didn't last long, I haven't seen any courses offering a free license (or even using Matlab for that matter), and to get the Student license you have to be enrolled at a 4 year institution.

In those classes that did use Matlab, there were quite a few people sticking to Octave, though it wasn't 100% compatable. And when I got to Ng's course, I (and I imagine a whole lot of others) were really happy to see he went 100% with Octave. Had he gone the Matlab route, the old course would be pretty worthless now.

We'll never know what happened behind closed doors, but I think Matlab was sponsoring some courses in order to get new people hooked on Matlab and it just didn't pay off.