I have a cat that barks and growls like a dog. He loves to window gaze at my front porch. When people approach while he is watching, he will growl and then chirp and spit. These noises get more deeper, as if he is attempting to imitate a dog.
Which we do have one. So, it is entirely possible he thinks he is the same species as my dog despite the obvious size difference.
The funny thing is, my dog is quite brave when she is outside. Inside, however... she is something of a scaredy-cat. She’s more likely to run and hide if someone knocks at the door.
It is quite amusing.