Omg you're right, it's probably one of his students!!
Short answer: yes.
Long, spoily answer:
The Association president is indeed one of his former students. She has an ability called "Promise" which basically lets her manipulate reality to some extent by sacrificing emotions and memories. The reason she was so keen to buy Jio's Portrait is because she recognized him as being someone she "erased." In other words, three of his students no longer have any memory of him (the fourth chose to keep her memories). As for the reason behind that, it's an even bigger spoiler, so I'll hold off unless you're interested.
I'm not OP but I NEED THAT BIG SPOILER
For ppl that read the novel, did jio ever meet his students again?? Tbh i have suspicions the one that trying to buy jio's portrait are one of his students, that's why the guild master said something like, that person who never interested in something suddenly try to buy jio's portrait makes him want jio's portrait more (cmiiw)