Greenland whaling from Mississippi?

From The U-Boat War 1914-1918 by Edwyn A Gray.  Page 234.  The cruise of U-151 into American waters in 1918.  

The U-boat continued her cruise south claiming more victims as she went. On one occasion they picked up a decrepit old sailing-vessel crewed by poor whites and negroes. Their captain explained they were off to Greenland on a whaling expedition and that the boat was owned by a number of poverty-stricken families in Mississippi whose livelihood depended on them. Once again von Nostitz showed genuine compassion and, after a brief hesitation, he agreed to let them continue their voyage unharmed.

This occurred in June 1918.  A mixed race crew was hardly ever uncommon in American naval and maritime history.  But a sailing vessel sponsored by poor Mississippi farmers to go on a whaling expedition to Greenland from Mississippi?  This sounds extraordinarily improbable.  

Possibly the incident never happened.  Possibly the crew lied to the Germans.  Possibly the Germans misunderstood.  Possibly Gray or other historians misinterpreted the records.

All possibilities but there is also the remote chance that it is all true.  

We are left with an astonishing claim and no resolution.