Answer and Explanation:
The Dust Bowl survivors were much closer to being refugees than to being intruders. By definition, an intruder is someone who enters a place without permission with the purpose of committing a crime.
The current definition of refugee, as given by the United Nations, is of a person who needs to leave their country due to violence, war, or persecution. The survivors of the Dust Bowl did not leave their country, but had to move inside it, which makes them internally displaced people, or IDP. IDP is a person who leaves their home seeking safety, be it due to violence or natural disasters, but this person does not cross the border to another country. Still, the premise is the same as of a refugee: the search for security, for basic living conditions.
The survivors may have been seen as intruders back then, but they were doing what anyone in the same circumstance would do. They were fighting to stay alive. They were seeking protection, and safety, just like refugees.