These responses are called whenever certain conditions are found to be true. These conditions can include different religion, opposite traits, title claimant, etc. They are not dependent upon the net opinion modifier. In other words, it doesn't matter if he has a net +100 opinion modifier toward your ruler if he is of a different religion or if he has a claim to any of your titles. His actions, however, are influenced by his net opinion modifier, so he typically won't plot against you if he likes you.
Some possible triggers for these types of messages:
Heretic
Religious Differences
Foreigner