Lamplad didn't hide his emotions and he couldn't control himself when things didn't go his way. He could have pretended to be obedient. Then rushed back to his cave and broke through into a mana entity. He could then use his new power to bring away more of her warriors or even challenge her for the position of park leader.
But he was foolish and impatient. She knew what he was up to immediately and was able to manipulate him easily. He didn't even suspect a thing and he still respects her. She had no choice but to be derisive of him.
To be fair, she isn't the only female who has been derisive of Lamplad in recent history. Tesrat was also derisive of him. He liked her but she didn't like him. He was too boring and thick-skulled. That's what Tesrat would always say about him.
