The issue with the Bond market (where the BoE had to intervene re pensions) caused mayhem in the UK Gilts market - in isolation that could be explained away, but there are knock on impacts for anyone remortgaging.
Gilt Yields are used to determine the cost of Fixed Rate Mortgages, and because of their actions anyone remortgaging was struggling - because not only did rates go up, many providers pulled rates entirely because of the uncertainty.
While its true to say that worldwide interest rates were rising, her and Kwarteng were pretty much responsible for average UK 2 and 5 year Fixed Rates jumping almost 2% in a month.