When an ambassador comes to me immediately after a huge event, I don't assume he's had the time to hash out the idea with the rest of the realm, and that realm with the rest of its allies.
I'll grant that the letter wasn't overly explicit, but can't say I expected that reaction either. Luria's always been touting about being a multi-faith realm where astroist leaders do stuff against SA interests, and D'Hara has a large portion of non-SA nobles as well, whatever goes on in SA is of no obvious interest to most nobles of both realms.
When an ambassador is throwing out ideas, they generally qualify that it is the case. Ambassadors/Diplomats live by words, it is their domain. They understand influence, inference and impressions. If I was the Lurian party in this, I would strongly believe it was Machiavel's intention to deliberately mislead me as to the status the proposal. It would be unthinkable that any diplomat skilled enough to be raised to ambassador has not learnt to say "This proposal has not yet been put to the realm and is not official" when starting discussions.
Any ambassador that is relying on the other parties assumptions to pass on such information is a rank novice. Its called qualifying your position, it is quite a useful concept.
