I've seen countless stories like this where they're genuinely this dumb/clueless/naive too, especially since I got into yaoi in the late 2000s where most of them were like this, but the bottom acting like he genuinely doesn't get what the emperor is trying to say in front of the emperor then turning around to the red haired guy and telling him that the emperor proposed to him shows that to a degree he only played dumb there. Some characters also described the bottom as if he was smart (we only saw the complete opposite; him being very dumb) so yeah I feel as if it's definitely at least hinted that he's just playing dumb.
How can a 24 year old be this dumb