FL200 is FL200, no matter what the TL/TA.
You are 100% correct. I'm not meaning to imply this was not a very serious mistake.
All I said, in different words, was that a pilot who is never used to hearing "Flight Level Zero Two Zero" or "Flight Level Two Hundred" could easily make a mistake for "Flight Level Two Zero Zero" or the other way around (which seems to be the case here).