Gelston is a village in the South Kesteven district of Lincolnshire, England. It is situated 2 mi west from the A607 road, 5 mi north from Grantham, and in the civil parish of Hough-on-the-Hill, a village 1 mi to the north-east. It is in the civil parish of Brant Broughton and Stragglethorpe.
Gelston is in southern England.
Based on the information provided you would need an unreasonable amount of geographic knowledge to say whether Gelston is in southern England or not. I would say given the context it is neither definitely correct or not.