She was also unable to leave. It is not uncommon for dogs to growl or even snap at other dogs who are in their space when they are on a leash or tie out because they do not have the ability to leave.
Also, alot of dogs are really rude and adult basenjis do not tolerate "rude" well. Many dogs rush up into other dogs' space which is very rude. So in the case of the Sheltie in the front yard, the provocation could very well have been the dog invading her personal space without her permission. The second incident could very well have been exactly what Pat said, her protecting her puppy pack member.