I am happy you got to experience this but I have serious concerns about your instructor. A DM, let alone a DMT, should never be conducting an OW course dive. Per the agency I teach for ,a DM (again, NOT a DMT) can "Supervise students while the instructor conducts a skill." This means if there is more than one student, the DM keeps an eye on the student(s) not currently doing a skill with the instructor.
Other than that, you are also allowed to "Accompany students under the direct supervision of an instructor during surface swims to and from entry and exit points, and during navigation exercises."
A DM should never be conducting skills in an OWC and certainly not a DMT.
You mentioned buoyancy is key for you but you then state the instructor was kneeling not far from you. If you and the student were both kneeling, I would suggest looking into training students neutrally buoyant and in trim. There are many resources out there as well as here on SB that talk about how to do that and why it is better than teaching on the knees, especially since we don't dive on our knees.
I am not trying to rain on your parade here. I understand your excitement but have to point out the major flaws as well as what I would consider massive standards violations by your instructor. This is meant to help you see where things are going wrong so that when you become an instructor, you do not make the same mistakes.