It was a puzzle for me too but I think you nailed it. I don't see any other explanation.

My bias came from a completely opposite direction. Here in Slovenia we have an undeveloped and under-funded movie industry which often hires amateur actors or theathre specialists, and we get this kind of acting routinely. To my eyes this is just how "local production" looks like. However, since everything else in Squid Game is so superb, this doesn't fit in.