It’s a reference to past immigration practices, probably too obscure for most people.
https://www.vox.com/2019/7/29/893484...o-dark-history
edited to add: The medical testing and treatment of border jumpers today is probably more akin to what our immigrant ancestors encountered at Ellis island. Anyone who looks sickly failed a TB test wouldn’t have been able to get on a bus to go to Martha’s Vineyard.