This was one of the most touching scenes in Frankenweenie. Victor truly admired and respected Mr. Rzykruski, and was genuinely sad to see him go. Victor was the only person who said goodbye to Mr. Rzykruski.
None of my teachers got fired in the middle of a school year, but if they did, I would have wanted to say goodbye to them.
Also, friendship does not have to be limited to peers who are the same age you are.