THE moment that Essaint said that the dungeon they'd be raiding was the Infernal Chasm, Luo Yan already suspected that he wasn't inviting them to join his team out of the goodness of his heart. He's quite familiar with the Infernal Chasm dungeon. He had done a number of raids there when he was playing the PC version. So he also knew the characteristic of the boss dungeon. Knowing that, it's only natural for him to get suspicious.
When they met Essaint's other two friends, Luo Yan's suspicion only strengthened. Especially with the attitude of that Bronzed Leaf. His eyes, while looking at him and Luo Jin, were full of taunts. As if thinking how stupid both of them were for agreeing to team up with them for that dungeon raid. He's probably already imagining their miserable expressions once the dungeon boss used his life draining skill on both him and Luo Jin.