That's some big assumptions right there. More than likely the letter just removed the advantages for PS and leveled the field with Xbox. Obviously, any roadblocks for GP inclusion would be removed as well. Which Ryan probably wasn't happy about.
I assume that Jimbo -and everybody- expected that if MS buys ABK then MS obviously would get this advantages of having them the marketing, exclusive betas, exclusive bundles, maybe timed exclusives for DLCs, locking it from appearing in non-MS game subs etc. And that this (plus to get the yearly ABK revenue and profits, teams and IPs) is mainly why MS bought them.
The roadblocks to include CoD on GP (like these other preferences) only affect the games already signed with Sony, which seems are already published ones plus according to rumors apparently the next 3 games. In RE Village that meant that for at least around 15 months after launch it couldn't appear in non-Sony game subs and that if Sony asked them to negotiate (giving Sony preference in related negotiations including first and last offer) to put it in a Sony game sub then it would expand and obviously it would expand if Sony signs to put the game on their sub.
Meaning that for games already included in the current ABK+Sony deal will be able to be in GP around 15 months after their release. And future CoD games not included in this deal could be there day one, and MS will be able to get their marketing, bundles, etc.
Ryan knew that because he signed that deal with ABK, or at least he signed the similar deal with RE Village. So what made him angry and find it 'inappropiate in multiple ways' should be something else.
I assume it's that MS told him "CoD will go exclusive once the Sony+ABK deal ends and if you want to get CoD 3 years more -with no option to extend it- this are my conditions: sign that you'll release all future Bungie, ND and SSM games on Xbox, pay me a gazillion dollars and make me a blowjob. Signed, Phil" and Jimbo told them "Oh, fuck you. Signed, Jimbo" (I'm kidding)
And then MS went to the press, to their corporate blog and to the regulators to say they planned to keep CoD on PS, that had a signed agreement with Sony about it, etc. If MS would have been honest and would have said to everybody 'we'll make CoD exclusive after its deal with Sony ends' or "after the deal we'll keep it 3 years more on PS and later will go exclusive" (and to sign this without demanding too much money for it) then I assume Jimbo wouldn't have said anything.