@WBYeats,
1. The conversation was amazingly indiscreet.
All those there engaged in the conversation, with the English guests revealing things that should have remained private or secret.
The teller of this anecdote passed this information on to Berlin.
2. The Chancellor was heavy -handed: would do and say things without thinking about other people's feelings, and about the consequences.
And he did, and made a remark that showed he knew what was said during that weekend.
But then, think the English, how could he know?
Well, the only German there must have told him! That is, it "took the trail straight up to me."
3. A couple of paragraphs earlier, they were talking about fitting into British society. Well, the British are sporting people - fishing, hunting, shooting, yachting. So, as Von Bork's cover as a spy, he poses as a great sportsman:
"You yacht against them, you hunt with them, you play polo, you match them in every game...You are a 'good old sport' 'quite a decent fellow for a German,' ...And all the time this quiet country house of yours is the centre of half the mischief in England, and (while posing as) the sporting squire, (you are really) the most astute secret-service man in Europe. Genius, my dear Von Bork-- genius!"