Maybe I did not understand. You and this lady who had never seen this dog before go into the backyard of his home, and feed him some treats. After checking how tight his collars/leads are, you head off for your car, and while you are out there, the other person trips on the lead.
Did she actually fall onto the ground? Did it yank the dog by its tight collar when this happened?
I guess I think it is a lot to ask, to have a chained dog meet some strangers in its yard and then have one slip and fall and possibly yank a possibly painful lead around in the process.
It is also possible that the low-life scumbag that owned him did more than just pitch him out in the back yard and hit the road. It is possible that the guy deliberately tried to make the dog protective. A lot of people don't socialize the dogs and even treat them harshly to try to make them guard dogs.
Cujo used to spend an hour every morning in the back yard on a chain. Some broad came by with treats and started feeding him treats from the Insurance Company parking lot next door. Cujo had all kinds of issues, medications and skin problems, and that was totally inappropriate. I understand that your situation was different, but if that lady freaked him (Cujo) out by tripping over his lead and he bit her, I would not have held it against him.
RIP Arwen, CD RN CGC
RIP Whitney, RN CGC
Jenna, RN CGC & Babs, CD RA CGC HIC (not AKC)
Heidi, RA CGC & Tori, RN CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear