@Stoner i believe Griselda already have a hunch bout that new guy purpose, she may have just been seeing how will he act from now on, i mean look at the way she glance at him, she definitely found him sus...but i bet she cant just kill him off easily since he has relation to Emric Knight iirc, but it will be different when he made a mistake that can serve as excuse to do him off
Y'know I'm going to preemptively blame whatever confrontation that happens next on Griselda and not the new guy.
She gave him the carte blanche to execute on the spot any "trespassers" and even said don't bother reporting it to her. She knows the majority of the country is still pretty racist/xenophobic towards Northerners (hell she did it too). She didn't bother telling the guy she gave a free pass to kill any "trespassers" about the fact that the new doctor they hired is Northern. It is also known by those in the know (including the new guy) of her bosses exploits in the Northern campaign hence a pretty solid reason for Northerners to seek revenge. Put all this together and from his POV a reaction like this is justified.