No he's wrong, as you well spotted.
If a plant (plant A) gives you 200 seeds or more, none of them are genetically the same. It's all thanks to meiosis. That's the point of sexual reproduction. Even feminised seeds are different from one another. They are a randomised combination of the parent's(') DNA.
So when you plant a seed from Plant A, that we will call Plant B, any clone you take from Plant B will still be cultivar (variety) Plant B. You can't go back, really, 'cause the DNA has been recombined. Any seed from Plant B will be Plant C or any other name you chose to give it. Just not Plant A or B.
Highschool biology.