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.