Bigfoot has had a long relationship with dogs. They don't seem to mix. Dogs usually won't follow the trail of a BF and will cower in their presence. Also dogs that do encounter a BF usually don't survive the encounter. One thought is the BF may see the dog, barking away at it as a means to lead someone to it. The dog gives away it's cover or location, so the BF takes it out. The other may be dogs just bother them.
In Arkansas the Foulk Monster was known to "tear the hide" off dogs and kill them. Hunting dogs would not chase it.
Another thought, dogs are after all a version of wolves, and BF has been known to interact with wolves and coyotes in a threatening manner. There are those, including myself, that believe Bigfoot will ambush a coyote pack and take their kill.
Domesticated dogs, unlike wild animals would act differently around a BF, either being brave and a nusience or just cowering and running away. It may be that BF expects them to behave like other animals and respect the Bigfoot and leave it alone. When the dog barks and challenges the BF he may react to that and kill it.
Bigfoot may see domesticated animals as too much a part of our world than theirs and since it shuns our world then the Bigfoot may be reacting to the dog adversly from that point of view. People tend to run away from a BF but a dog may challenge it, and thus give the Bigfoot the need to destroy it. I wonder what would happen if a human challenged a bigfoot?
And lastly, it could be simple food. A dog, especially a domesticated dog would be rich in proteins and a nice catch. If the dog has been fed well the Bigfoot may see it as a prize and healthy catch. Maybe they like dog meat? They appear to like deer, coyote and wolf. And since there are more dogs than wolves, well... do the math. I would suspect it would be eaiser to catch a domesticated dog than a wild wolf or coyote.
I know my dog is friendly and would probably run up to a Bigfoot and want to play! LOL
This doesn't necessarialy mean the bigfoot is aggressive. It may just be a defense of territory and a chance for a good, easy meal.
These are things that we need to know, and why field research is so important. Questions like the above will be answered one day, probably after one is captured or killed. But until then we need folks in the woods following the few patterns of these creatures and studying them. This is where we can do our part.