That's not the part I mean. His substack article asserts that Canada and others started selling off their US debt holdings based on absolutely nothing.
It references a tweet from Mar 11 (which was wrong https://www.thecanadianpressnews.ca/fact_checking/online-posts-claiming-canada-offloading-400-billion-in-u-s-bonds-are-false/article_4b46bf68-1fa5-5eeb-8e5f-fd8e6b7e80bd.html).
The only real suspicion serious people have is that possibly China is doing a sell-off.
The entirety of Blundell's story is based on "Wouldn't it be cool if this completely fabricated thing is why bond yields went up?"