My humble opinion is that the root of this was a poor pre-flight briefing.
I recall once flying out of Mumbai, the ground controller kept saying number one at the end of the taxi routing (3 times maybe, I read it back each time). Both the captain and I shrugged it off as it being a silly Indian ATC custom. Until we started approaching november one (the hold short as it was). Yes, our mistake being not fully briefing the entire expected taxi routing.
So being in a foreign place and "when in Rome" is my best guess as to what happened. That being said, the people saying that being American with a TA/L of FL180 so therefore hearing flight level two hundred was new to them.. even as a fairly young F/O I find it hard to mix up two hundred and zero two zero or two zero zero.
It seems like a chain of errors that started with a poor briefing regarding the TA and MSA.