It's in the panel texture buffer, so unless something really bizarre is happening, it's being rendered by the 733's custom instrument code. Why? Only @tkyler can answer that.
P.S. I hope in the future the pixel density for the instruments is increased (though as these are meant to be CRTs--I assume--it would come down to what's necessary to give it an authentic analogue look, which probably involves a shader also), possibly when LR provide the custom avionics API?