I dont believe it and you said it yourself....

"This was a Bank of England problem, which they conveniently attributed to Truss and Kwarteng."

Exactly; the Truss proposals gave the banks and markets severe indigestion and so they blocked it and blamed Truss for the failure of implementaion. It was quite a remarkable revelation for me to see how that hidden power worked. Once the market herd had turned, she was toast.