i can't imagine the BO finding about akai from such a dumb scenario, but someone's gotta see him since gosho made a point of not disguising him. sera isn't around this time, so could it be haibara? that would be awesome. other not as exciting possibility is yumi.
i think the guy blended the coffee to heat it up since blenders produce heat and it would make sense that chuukichi would touch a hot blender and have that reaction. you can't really use the toaster or blender to heat bread, or use ice cubes to keep ice cream cold. also 10 min seems just about enough time for him to heat the coffee, kill the guy, and pretend to walk out. i don't know how the fire happened, he could have used some sort of timer device but there are no hints about that. i also don't know what the point of the gacha machine was. and its also a bit weird that he could have predicted that they would put their bags on the stove.