I was under the impression that we weren't given any indication in the books whether this prophecy was Seanchan or not. I don't have my books on hand (I've been using encyclopedia wot), but as I recall, Tuon doesn't cite where she heard this prophecy from. It very well could have been an original Seanchean prophecy (assuming I'm recalling correctly, which is questionable ).

If it was from the Karaethon Cycle, however, it is likely corrupted. The Guide states that Ishamael gave Hawking's son a parting gift of an "unspoiled" (read 'corrupted' ) version of the prophecies to take with him to Seanchan, passing that corrupted knowledge down.

Of course, the issue is muddled even further by the fact that their were existing Seanchan prophecies that were around before the Hawking's Son conquered Seanchan, and by the fact that Damane foretellings were added in as well.

Here are Brandon's comments:

Q: "We know that the Karaethon Cycle and the Essanik Cycle are different. Is that because there were different contributors to each, or some other reason (like tampering by Ishamael)? Which is more correct?"
A: "The Essanik cycle had only in Seanchan and there were different contributors. Which is more correct? I’m not going to say which is more correct. There has been tampering…"
Q: "In both?"
A: "People are not perfect, alright? Let’s just say that and there are lots of forces at work. The Essanik cycle, they have tried to preserve it as perfectly as they can. If the Outriggers ever get written there will be more information about what the Essanik cycle is. It is had only in Seanchan. It was given by damane in Seanchan, so nobody knows about it on the main continent."

And:
Q: "Did Ishamael have a hand in how the Seanchan prophecies have come to differ from those of the Westlands?"
A: "RAFO."