Red button is probably a double entendre here - you press the red button to record, so he’s poking fun at RDS’s Twitter glitch. Red Button could also be code for the nuclear launch button. And Red Button could also refer to the size of his base (and/or his campaign button). Among other allusions. Maybe he likes Comedy and has some Red Buttons paintings.
The NK remark is a little more oblique, a reference to Trump’s detente policy with NK during his term and to RDS’ lack of foreign experience.
I agree this post strays from Trump’s usual directness.
Actually, the “red button” talk is a call back to when he originally responded to Kim Jong Un’s nuclear posturing: