Originally Posted by Backinstyle
Taken from google about characters acting out of character.

[When a character acts out of character, what this really means is that the writer has failed to sustain the causal believability of his character's actions. And the result? Readers become distanced from the character, and their suspension of disbelief is, at best, endangered.]

This is what we mean when we say out of character. His writing is unbelievable in act 3 regarding SH and Halsin.
Cherry picked and informal definition. Because characters evolve, it is impossible to tell how their opinions may or may not change. The author will always set the limit. You're free to use it in any way you like, of course. "Writer does not understand their own character" is unfortunately the default and I have had enough of it.