They may act like humans do when we dream, and their brain activity while they sleep looks similar to ours when we dream. But neither of these facts allows us to conclude that they're actually dreaming.
The verbal reports are key to our shared understanding that most humans experience dreams when sleeping. We do not have this for dogs or any other species.
We only know that humans dream because we tell each other about our dreams. There's no evidence that any other species dreams, as they don't tell us about it and we don't have access to their qualia.
The verbal reports are key to our shared understanding that most humans experience dreams when sleeping. We do not have this for dogs or any other species.