He learned that so fast and I really want to know what else he can learn in even longer amounts of time while also keeping a classical approach (Beethoven, Chopin, Liszt) (NO BACH).
I'm not too big into Bach myself, I see him as really overrated and not needed. If he wants too study Bach at his own house that's fine with me.
IMO this attitude is not setting a good example for your student.
Many who have been around music for a long enough time, whether they be professional or amateur, will experience a situation where they have to learn a piece of music they do not particularly like. One could rant all day long about dislikes and grievances of the piece, or one could learn the music, present it professionally and move on. How one chooses to proceed could mean the difference between getting paid for a job, or not. It could also be the difference in being called back for more jobs, or getting recommended to other people for jobs, or not.
Bach is not one of those composers that one should take such a trivial attitude towards. If your student decides to pursue music seriously, there will come a time where Bach will be required for an exam or audition.
There is a difference between having an opinion about certain music, which is completely fine, and withholding part of a student's education just because the teacher has a certain opinion about music, which IMO is irresponsible and professional negligence.