It makes all sense and Govv makes the right conclusion from the statements.
The fish wanders from their birthplace in East Othard to Thavnair and further to Eorzea and grows on his way.
They use the opposing way to make the conclusion easier to understand.
Eorzea: giant size -> Thavnair: medium size -> East Othard: small size
But all 3 are the same fish on all 3 places but on different times in the life cycle.