Yes, Malleus is being a brat. For Lilia, this likely does not come as a surprise, but these days, he tends to behave at least a bit less childishly than he had growing up. Malleus keeps the can away from Lilia's grip, secretly pleased with the attention he's getting. Is this the way to get Lilia from his silly 'computer games'? Tsk.

"Why do you need this? Do you not think a healthier drink would be a better option?" The squirming is back, but Malleus does his best to ignore it.

Honestly, it is risky to ignore Lilia's demand to give it back, but Malleus does not particularly care.