That is actually good news. The Gross family from London has this Y chromosome type E1B1a. They also settled in Maryland. John Gross sponsored a group of settlers to go to Virginia and Maryland in 1721. He came from London but his ancestors were probably German or French. This family are associated with Gross's corner in Virginia, and Gross Mountain and another Gross's corner in Maryland. Some descendants live in New Zealand and Australia.
They are the only Gross family that I know of who actually owned plantations.
At least it gives a couple of places where your family probably lived.
The other possibility is that the people were named after the owner of the plantation but he wasn't their biological father.
I was also quite surprised (and somewhat relieved) that there were very few African American families who matched me (about three), and these ones were descended from those Welsh slave traders I spoke about named Williams and Lewis.