I am lecturing a class in which a student has asked for my slides in advance. (My main reason for not doing this is to avoid students passively reading the answers to questions that I put to them in class.)
The student writes
Please upload slides before lecture; we need to take notes on the slides. A good lecturer can always decorate branches with leaves and flowers, so don't worry if someone read slides before hand
Leaving aside the metaphor of "leaves and flowers", I read the statement in the second sentence as equivalent to
A good lecturer would make slides available in advance.
...with the tacit implication that a lecturer who does not make slides available in advance is a bad lecturer.
What logical fallacy or fallacies may be occurring here?
(P ➡️Q) ➡️(~P ➡️~Q), then you're after denying the antecedent. Otherwise, you might have a false dilemma (there might be more than one way to be a good lecturer).