Hello, I am Vietnamese.
I also question myself whether or not Lung is a name???
It is quite awkward.
For 30 years in my life, I have not met anyone who names Lung - Lùng - Lứng - Lửng.
Though there still be two options.
Firstly, it is a wild animal name Lửng (picture below), but nowadays we don’t name after an animal anymore.
Secondly, probably Lung belongs to some ethnic minorities living far from modern cities.