I'll let Dr. Yaruss answer the first half of your question (I hadn't seen that paper), but will respond to the second half. There's strong evidence that stuttering is a neurodevelopment disorder. It can't be caught or given to someone else in the way you describe. That said, envionmental factors definitely play a role in how someone copes with or responds to stuttering. This is basis of a lot of childhood treatment, which may try to improve attitudes or decrease time pressures, but a person's environment is also likely a factor in developing less adverse impact related to stuttering.