In the experiment, then they did everything they could to remove their owners scent from their home. The dog's owner came home at the usual time, but the dog wasn't expecting it this time because they had removed the owner's scent earlier, so the dog was clearly surprised and confused.
Dogs have a very strong sense of smell which we humans often fail to appreciate. It's not like dogs can smell their owner coming home from miles away, that's a little preposterous. But they can use their sense of smell in other ways, which are not so obvious to us, such as to maintain a sense of time.