First of all, I'm not sure why people even bother using Twitter if they want to make nuanced and lengthy arguments. It's a useless medium for that. He's not the first person I've seen to do this, but I certainly have very little patience for someone making arguments by chain Twitter.

Terrible choice of format aside, the guy is spinning Russian history to give it a pro-Ukrainian angle. I would take issue with most if not all of his characterizations, such as saying that the growth of Muscovy was due to "brutally conquering" other states. There were a few competing states that were conquered by force, but a great deal of the land Muscovy got was through inheritance following intermarriage, feudal pledges of fealty by small and weak states who needed protection and in some cases, purchase.

Also, I strongly take issue with his use of "Kyiv" as the name of the capital of Ukraine. It was Kiev in all the old chronicles - Kyiv is a modern name. It would be similar (not a perfect analogy, but useful nonetheless) to calling Constantinople "Istanbul" when talking about it c. 1000 AD.

He's also done a really shoddy job of explaining Russian learning. This is the same old tired theory about "not having access to learning" that I've heard from older sources. The problem is that it really ignores the reality of the situation. First of all, Old Church Slavonic was not so different from Old East Slavic (the predecessor of Russian) that people needed specialized training to understand it. I recently read a somewhat dry 800-page book about the history of the language and the differences are really not that strong. OCS was slightly different, so the OES gorod (city) became OCS grad, OES golova (head) became OCS glava, OES bereg (riverbank) became OCS breg. A lot of words didn't have complex consonant clusters is OES, so OCS nadezhda (hope) became OES nadezha. The conjugation system was slightly simpler in OES, but the OCS forms were recognized.

[EDIT: Let me add that I learned OCS in a couple of days based on my knowledge of Russian. I'm not sure if that was clear. Some of it can be read by any Russian speaker, but even the parts that need to be explained can be quickly and easily explained and isn't something that would take any significant expenditure of effort to learn]

Not only that, but all the monasteries were translating works from Greek into OCS/OES (creating a hybrid language that would become Russian). They had access to Greek philosophy and non-liturgical works. Not only that, but educated people in the court and monasteries in Muscovy learned Latin. The myth that Russia didn't have access to Western learning is just that.

The real difference is that Russian xenophobia made them suspicious of much of this learning. It took Peter the Great and other leaders (like Catherine the Great) who dragged Russia kicking and screaming into modernity.

Certainly, the choice of Orthodoxy meant that the church wasn't run from Rome, which later in Russian history meant the Church was subservient to the State (though in Muscovy the opposite was really true - the Church was if anything dictating terms to the tsars earlier on, and the Church perpetuated the rule by Mongols and Tatars because it benefited from the Mongols' disinterest in spiritual matters both economically and politically). However, this choice is again a reflection of a light xenophobia. Even had Russia accepted Catholicism, arguendo, it would have broken away early on because there was a high level of suspicion of outsiders.

That, by the way, is something that is common in "border areas" that are the object of constant invasions and attacks. I would argue that the geography shaped the culture, which shaped the choice of religion.