In my observations, cats have three kinds of bite. There is the love bite, which is usually accompanied by head butting or cheek rubbing. These are very gentle requests for petting, or sometimes just shows of affection. There is the attack bite, which inflicts damage; most indoor cats will never have cause to use one, although outdoor cats may use them in fights with other cats or hostile animals. They can leave very nasty wounds; they are well-equipped predators after all.
In between is a bite that I call the "You're really starting to get on my nerves now; stop annoying me" bite, which is somewhere in the middle. Not forceful enough to draw blood, but forceful enough to really pinch, this is the resort of a cat feeling stressed or bothered or ticked off (or sometimes physically ill). Sometimes this bite will be accompanied by a swat of their forearm with claws partially extended, but not at maximum strength. Most owners may have gotten a couple of these bites and swats in the lifespan of a particular cat, but a good owner who understands cat culture will know how not to annoy a cat and may very well never incur them. But it is hard to completely avoid them forever. Even good owners may get one if they fall for the old "belly rub trap", but a really relaxed cat will often stop resisting belly rubs at some point.
I would put this particular bite in that middle category. Clotso is exactly the type who annoys cats. She talks to them wrong, touches them wrong, stresses them out, and gets on their nerves. I forget exactly what was happening at the time, but I dimly recall it being nothing; she was just doing a typical stream and going into her chubbyuse routine. She reached back to pet him, and he gave her the warning bite.
I have never witnessed abject fear or open hostility from her cats. She did feed them, which counts for a lot with cats. They tolerated her. However, I never saw any particularly affectionate signs from her cats either. I think the cats could take her or leave her, but since she was the great food mama, they mostly put up with her.
That doesn't excuse the abhorrent neglect she showed for their health and well-being; since they knew no other life, they didn't really know how bad they had it. Buster the Dog hates her more than the cats did (he may see her more as interloper than family). But the cats didn't seem especially in love with her either. Sam bit her more than just that once, although it was often off camera. She'd talk about getting bit sometimes, and it seemed to happen more often to her than it does to other cat owners.
Feral cats tend to lack some of the etiquette domesticated house cats have, and they may decide to chomp on you and scratch you more readily. I hope Julia beats her up one day.