The animation building is where most characters make their debut. Even Anna & Elsa started out there before quickly moving over to Epcot.
I wouldn't be surprised if an Olaf M&G is for a similar purpose. Draw crowds to a park with limited options and also prepare for a permanent M&G in Epcot.
Huh? The comment you quoted is referring to Inside Out going to Imagination (since Olaf is going into the Animation space).
I may be wrong, but I don't believe Anna and Elsa were ever in the Animation Building.
Olaf is obviously being shoe-horned in there because he needs a M&G and they have a place available.