When the lizard possessed by "Algae Scale" Dodd arrived on the scene, Xia Nan was lurking aside, observing as per the plan briefly laid out with his teammates.
Because of this, when he witnessed the way the other looked at his teammates, Xia Nan was sure—the newcomer could not be Alton.
From the perspective of the coastal reality world, he could see Xia Nan, enveloped in blue light, floating in the air above the sea, knowing he was still in the Secret Realm.
With Alton and Dodd's spots overlapping for an extended period, they have likely met each other. The little guy could not possibly mistake himself as the last remaining force within the Secret Realm according to perception.
Also, he would never show such a bloodthirsty and excited expression to them, which was not Alton's character.
But to be honest, if the lizard before him wasn't Alton, and Xia Nan had to consider it as "Algae Scale" Dodd, he would be skeptical.
