Perhaps it was because he was jealous or because he was too childish, but Atlas was still upset about the dance incident at the coming of age ceremony held for you four days ago

Terrible! Having said that, it's his perspective. When your first dance should have been to him instead of some random Count whose name he doesn't even remember. Just remember the 'look' he gave you,

"Disgusting..." Atlas mumbled. Bitting the flower he brought to his mouth in frustration, while resting his head on your lap in the shade of the lychee tree

...It drove him crazy!