With the more information you have provided, I honestly don’t think your dog nipping once because someone stepped on him, or because there was a strange, unexpected man in your home, necessates an extreme reaction or extreme problem. I feel like the unexpected part plays a major role in this. Would he had been fine had he been introduced to the man beforehand? Or in other words, does he do fine with strangers in the house that he is introduced too?
My grandparent’s dog was a sweetie, and did really good with strangers. However, there were two times she went and nipped a stranger (maintenance person and a friend that hadn’t been around for a long time) inside the home, and it was because they came over and tried to pick up my little sister and I or did a large hug/pick up thing of my grandma. She nipped because she was protective, which sounds like your dog did as well. Not saying it’s okay for dogs to bite because they are being protective, but it is certainly different than the image being created before that your dog had attacked a person out of nowhere and little harmless old lady.
My dog would also growl and snap towards my cats when they would crawl or jump on top of her when she was sleeping or otherwise distracted, because it startled her.
I would agree this sounds more fear-based. My dog will “nip” (she sorta does this growl snarl thing and snaps/bites the air, but never makes contact with) when we are walking down the hall in our apartment building or outside on the side walk and turn the corner and someone runs into her. She just get’s really startled and scared when someone runs into her, which I can understand.
I feel that it is almost a normal dog reaction to try to snap if in pain (ie being stepped on suddenly, especially if it was hard), or if they are let out of a room and there is a stranger in the house. That doesn’t seem to be aggression, but more being startled/afraid/pain and protective of you and her home. All 10 dogs (german shepherd collie mix, white shep, border collie, hound mix, eskimo mix, lab mix, cocker spaniel, corgi mix, spaniel mix, etc) I’ve grown up with/interacted with a lot have the reaction of turning and snapping if you accidently step on them or sit on them or something.
Also, I would’t mind seeing a pic of him, if you care to post one 🙂
EDIT: Reread your posts, I definitely think that he nipped the pest control man because he was startled and thought he was a threat to you, especially if you had nervous energy about him being in your home that he could feel.