Fortunately it doesn't appear the teen infected anyone else. But we don't know the source of their infection. The virus is similar to the avian flu circulating in wild birds.
What keeps avian flu a low risk at present is humans lack the receptors in our upper airway that would allow efficient transmission. But H5N1 could potentially acquire mutations that allow for efficient transmission in humans.
At the individual level, we can do our part by getting the seasonal flu shot this year. It won't protect against H5N1, but it will protect against seasonal flu co-infections.