Levi had watched their interaction with cautious interest. Everything that he had heard about the Aquarian said that he was cold and aloof.. That was Not the Merman he was watching now.
He was fidgety, talkative, and smiled at Iris often. When she quipped at him, he became flustered. Levi doubted for a moment if he was watching the right Merman, but there was no mistaking it..
Levi could smell Triton's blood within him, so he knew right away who 'Trident' really was, once he got close. The Merfolk were all technically descended from Triton, but Atlas' family was special.
Several fated connections with Undines, Gorgons, and the other kingdoms over the eons had made his own family's connection to Poseidon stronger than the other Merfolk. Making him easy to spot.