Iraq as in the country? Is it a korean idiom or something?

The idiom is 'dumb as a rock' but he obviously said it wrong which is why the teacher was laughing so hard

if you think about it, the word ‘iraq’ is pronounced similarly to ‘a rock’ so heechan must have confused the two terms.

Oh. I'm as dumb as he is

I was soo confused too, my first language is Spanish and Iraq doesn't sound anything like "a rock" so I knew Heechan got it wrong but I couldn't catch the joke at all lmao