Hear me out, although I am probably mixing MDZS-verses (novel, drama, etc), in this case it does not matter so much.
No one should be surprised that WWX did not know the meaning of the Lan ribbon, his poor memory does not play a role here - rather, his working methodology.
My bet is that WWX didn't rewrite as many Gus Lan texts as he should have for the punishment.
The basis of WWX's character is to work smarter not harder (and don't get me wrong, he is hardworking, but not in his work ethic, if something can be done easier he will do it easier).
I've seen many times how the fandom says that WWX invented the copying talisman, but no one uses it to explain his low knowledge of Gusu Lan customs, which is perfect solution for it.
Knowing the Lans their texts were written in difficult, serious language, if I were WWX I would rewrite them once, not focusing on content, just calligraphy - legibility, and later I would copy my version enough times and then wait the punishment off while doing other things to make it look like I did everything myself.
Especially noticing the scene at the end of his punishment (with the porn book), nowhere does it say that they checked how much he had written in a day (or at least I don't remember - they were keeping an eye but besides it?), even LWJ was surprised that he had already finished the rewrite and had time to tase and draw him - at that point LWJ's crush was unlikely to be so strong that he could overlook that.
Additionally, to deflect the argument that WWX knew the sect's rules and could recite them from memory. He could because LXR recited them during class (probably more than once), and WWX seems to be the type of person who finds it easier to ignore writing than hearing words (as listening is more closely associated with experience). Though again, in the case of the rules themselves, it's likely he's seen them on the wall enough times to remember quite a bit along with the help of LXR's recitation.
