The curled posture.

A person hiding in a vessel would naturally draw themselves into the smallest possible shape to fit inside it.

The curled posture of the remains is consistent with deliberate entry while alive.

The absence of rescue or recovery.

In most ancient catastrophes, survivors would search for and retrieve the bodies of people they knew.

The fact that this person’s remains were not recovered suggests either that no one knew he was in the jar, that the structure’s collapse sealed his location, or that there were no survivors in a position to search for him.

The objects accompanying the remains.