That was supposed to happen in a planned side-story game called "Biohazard Dash". Characters were supposed to find another hidden lab underneath the rubbles of the mansion. Infected plant-based enemies were supposed to be the focus of the game. Ultimately the idea never got past the planning/design stage.
As for the mansion, the Arklay Mountains were some ways away from the city, so I doubt the rubbles of the mansion got caught up in the explosion.