>> elevated inflation levels were transitory in 2021But… > that was correct?

No, it wasn't correct. By "transitory" the Fed meant "no need to do anything, inflation will go down on its own". It didn't go down on it's own, and the Fed had to act, too little too late, which is now causing prolonged inflation problems.

> It went up, then back down, due to a very unusual (almost unique, thus far) external cause.

The cause wasn't external, neither unusual nor unique, it was the Fed's start of interest rate increases, precisely at the time the inflation trend reversed.