The latter yes. As Pyxis said, backyard chooks are kept for personal pleasure and companionship, just like other pets.
The "hard part" of meeting that definition is looking at the meaning of "extensively and historically". You'd need to look at the incidence of suburban chicken keeping to determine how "extensive" it is in your area. "Historically" might have had a better chance of being established in the 1940s (or whenever) than it is now, but again, you'd need statistics and information as to the pattern of backyard chicken keeping over time. When I was a kid, it was IMO "extensive" because everybody had chickens. Now, in my experience, few do.
If the crux of the exercise is to show that chickens are pets and not farm animals, I'd be digging out all the info you can find about the incidence of backyard keeping in your area. My gut reaction - no, "extensively and historically" chickens are farm animals.