Why did the Seanchan hang the watchers?

Question

As the Seanchan invaded Falme, they hang the watchers of Watchers over the wave because "They watched for the wrong thing". But what is the right thing to watch? It seems to they were watching for the right thing and the army the Artur Hawkwing sent across the ocean did come back.

From WoT Wikipedia:

The Watchers Over the Waves - A group who believe that the armies Artur Hawkwing sent across the Aryth Ocean will one day return, and so keep watch from the town of Falme on Toman Head.

From The Great Hunt, Ch 29

Falme stood on a spit of land at the very tip of Toman Head, with nothing further west of it except the Aryth Ocean. High cliffs ran to the harbor mouth on both sides, and atop one of those, where every ship running into the harbor had to pass under them, stood the towers of the Watchers Over the Waves. A cage hung over the side of one of the towers, with a man sitting in it despondently, legs dangling through the bars.

“Who is that?” Domon asked.

Caban had finally given over sharpening his sword, after Domon had begun to wonder if he meant to shave with it. The Seanchan glanced up to where Domon pointed. “Oh. That is the First Watcher. Not the one who sat in the chair when we first came, of course. Every time he dies, they choose another, and we put him in the cage.”

“But why?” Domon demanded.

Caban’s grin showed too many teeth. “They watched for the wrong thing, and forgot when they should have been remembering.”

Answer 1

First Watcher is the title of the head citizen of Falme. The title originates from the Watchers over the Waves, and the job of watching for the Return, but over time the people have forgotten about that and just use First Watcher as a title. That's what they're being punished for.

Answer 2

I have my own theory on this. I believe that they were left there as original followers of Artur Hawkwing and were intended to watch for The Forerunners’ return so that they could be welcomed and the way made clear for them. However, unlike their kin across the ocean, they forgot (an easy thing to do over 1000 years) their purpose and were therefore punished for their dereliction of duty.

I believe there is more than sufficient evidence for this position. You must remember that the Seanchan consider everyone on the East side of the ocean to be in violation of their oaths and make them “reswear.” This implies that not only The Watchers, but everyone in the East has broken their oaths, but it was the one job The Watchers had, hence the higher price of failure.

I think most readers, as well as the people East of the ocean, assume that they were set there to guard against AH’s return, but the context leads me to believe the opposite. That is why the Seanchan punished them.