Finally Iberia have issued a press release about the launch of MAN-MAD (and also GLA). The release included this rough translation:
"Both routes serve both for point to point traffic between Madrid and two cities, and to bring traffic to the long-haul network of Iberia, particularly significant in the case of Manchester, the second city of United Kingdom and an important financial and cultural center"
We don't want to go down "which is the 2nd city" scenario again but that's an interesting observation from an airline!