And how do you propose we outmaneuver him while he already knows to expect retribution?

[Kylo Ren isn't exactly the most unpredictable, in terms of behavior patterns. She's got it in one: his anger is a low simmer, threatening to rise to a boil without somewhere to direct it -- without something to take it out on.]

He is not Force sensitive. The only other way he could have known was a confident guess.

[If nothing else, Loki and others have taught him that even false confidence can go a long way in unearthing the truth of things -- he'd never needed such tools with the Force at his fingertips.

Regardless: whether or not Thrawn knew at the time of his proclamation, he certainly knew now.]