This doesn't pass the smell test. If you teach a class of 250 students, you aren't even aware of the bottom percentile until the first exam is graded. That's many weeks after you've already taught many lectures. So how would your uncle even figure out how to tailor those initial lectures to that bottom percentile?

Where this matters is in something like a lab or music practicum where the communication between instructor and students is the class. But I can tell you from experience that the variance among different years of students in a single university is large enough to disprove your uncle's point. I had one class that could have been confused for graduate students. Yet another might as well been sent by the Trump administration with the goal of destroying the institution of ear training.