Probably because seeing that also made her emotional about him. And even another Pacifista is triggering it.
Again you guys bitch each chapter since Whole Cake Island your opinions are crap.
In my opinion, I rather see King and Kaido's relationship as platonic blood brothers. I really think King sees Kaido as the older brother figure that's always been there for him. And again I do think Kaido treats him as a guarded little brother.