The class wasn't a good fit for you. There's no need to judge beyond that.
The people for whom it was a good fit will come back to the class, and the ones for whom it wasn't a good fit will not.
You don't have to make any other judgement of the teacher or of the students who would appreciate that type of teacher.
Personally, being a disabled woman of 300 lbs with a large belly, with balance issues and being a person who learns physical moves very slowly (I've NEVER, EVER at any weight been able to keep up in an exercise class) and being a person who is somewhat intimidated by very fit instructors who often don't understand that or how I may need to modify moves, this guy sounds like he might be the perfect teacher for me, especially for the first class.
I wouldn't be put off by a first class like this one, though I would expect the teacher to spend less time talking in future classes.
On another note, I am always excited to see or hear of a fitness instructor or personal trainer who has an imperfect body, especially a VERY imperfect body. There are so few role-models of ANY kind for the less-than hardbodies. It can leave the impression that physical activity is only suitable for young, fit, pretty bodies who CAN keep up with a typical exercise class.
Even with my education (master's degree in psychology) I seriously underestimated the value of having active role models who look like me. When I lived in Illinois, I almost never saw very heavy people exercising or being active in public. Whenever I tried to be active in public or at a gym, I was virtually always the fattest, most out-of-shape person.
I tried not to let it affect my motivation, but it did.
In northcentral Wisconsin, I was absolutely astonished how common it is here for even extremely fat, elderly, and disabled people to be active. You see very, very old and fat people biking, hiking, swimming, camping, kayaking, geocaching, hunting...
At first I was awestruck and dumbfounded, but it wasn't long before moving my body seemed like an ordinary, even natural thing.
Sadly, I had never before felt that way as an adult (and rarely as a child, having been obese since age 5).
It's astonishing to me, what a difference seeing nontypical exercisers has made, for me in my own efforts to move more.
So, even though this instructor wasn't right for you, he might have been perfect for some (or a different group) of students.
The best teachers can modify their teaching style to accomodate a wide variety of students, but I find that kind of teacher very rare. Instead the student usually has to find the type of teacher they can learn best from.
This guy isn't the teacher for you, but he might be the perfect teacher for me and others like me. Maybe I'd find him boring too. Not everyone who teaches, is cut out for teaching, but you don't have to judge that. You only have to make the judgement for yourself whether he's the right teacher for you.
Just because you got nothing from the class doesn't mean everyone else had the same experience. If you were the only one who left, even 20 minutes after the class was to have ended, I would suspect that many of the other students were getting something from the class.
I have taught all sorts of classes (even a few physical activity-based when I was younger), and I can tell you how rare it is for adults to stay when a class of any kind runs over. There are ALWAYS some who will leave the SECOND the class is supposed to be over, so I'm inclined to believe that those who stayed were getting something from the class.