He glosses over the fact that native Ukrainians in those regions were displaced in the 1930s during the Holodomor and replaced with Russian settlers. That might explain why Russian sentiment in those regions is high.
The problem with that argument is that Crimea had been considered a part of Russia as far back as about the founding of the United States, and prior to that had nothing to do with a Ukrainian National project. Crimea isn't even mentioned by name once in the Wikipedia article you linked. Why would they be targeted as Ukrainians at that time?
https://en.wikipedia.org/wiki/1954_transfer_of_Crimea