They were entirely wrong about mechanism of setting the interest rate through the discount and fed funds rate, but this description also isn't comprehensive. The feds buying of treasury bonds isn't just to push them down, but is also a mechanism for increasing the monetary supply through the expansion of the fed's balance sheet. This mechanism for increasing the monetary supply is also why the linked article doesn't appear to be accurate either, as they don't seem to understand that the fed does have the ability to manipulate the monetary supply through its balance sheet.