Sanji #1 fan here, I can argue that.
Character development means the author gives more details to a character, from plot involvement to adding backstory to show a new personality to describe a trait to whatever.
Sanji-Stussy panel is a development no matter how minuscule it is.
Yes, the fawning & simping is just the usual, no development there.
But now Sanji and Stussy recognize each other, it expand Sanji's relationship connection. This is the part.