I'm sorry if this has been talked about in another thread, I did try searching but was unsuccessful. I was just rereading the official website for information on Othard, when I read this:

In subjugating Ala Mhigo, van Baelsar employed subterfuge to stoke the fires of civil unrest, a masterstroke which led to the nation’s capture without the need for a protracted siege. However, the unanticipated appearance of a primal shortly thereafter prompted the Empire to halt the legion’s advance. The legatus has since remained in Ala Mhigo, where he rules as an imperial viceroy.
Source: World, threats, The Black Wolf.

Is this misinformation referencing Midgardsormr? I don't think so, as the website also states this:
In the Year 1562 of the Sixth Astral Era, five years after the invasion of Ala Mhigo, the Garlean Empire finally rose from apparent inactivity to resume its attack on Eorzea. A fleet of airships was deployed to Mor Dhona, led by the massive flagship Agrius.
As the imperial fleet advanced into the skies above Silvertear Lake, the largest inland body of water in Aldenard, it was met with a wholly unexpected sight. Midgardsormr, the dragon deity of the lake, had arisen, summoned by a hand unknown.
Do we know what primal was summoned near Ala Mhigo?