You know what I had to think of? Lehndorff's mention of Peter's "English manners". If, as Fritz says in his eulogy, Knobelsdorff regarded courtesy/social trappings ("complaisance" in the French original) as an inconvenience, he might have liked it if Peter had a more direct style perhaps.

I like this hypothesis! Particularly if Keith, as Lehndorff indicates, was nice and friendly and not confrontational in the content of what he said, he just phrased things in an English (more direct) way. I could see Knobelsdorff getting along with someone like that. (Especially if Peter didn't tell him how to do his job. :P)