It’s discussed in the article, though it really should be given a different title because of that.

The fact that Asobo is the developer makes it much more impressive. A Plague Tale: Innocence is probably their most technically advanced game (and their...uh...”Rat System” that can handle thousands of rats on screen at once is technically impressive) but it’s nothing like a flight simulator. The article discusses some of the support studios they worked with to develop MFS, which again makes it even more impressive because I don’t think they had much previous experience successfully managing a bunch of support studios to produce a complicated product.

11 seconds into the trailer of A Plague Tale demonstrates what, I believe, Pulcinella is referring to as the "Rat System":

https://store.steampowered.com/app/752590/A_Plague_Tale_Inno...

Well that's straight out of my nightmares. Thanks for sharing.

what is the role of the publisher? Why can't Asobo simply market the game?

Publisher pays for making the game, and pockets a proportion of the sales revenue.

They normally bankroll and distribute the game.