The timeline for the destruction of the house doesn't work out. McPherson, not Sherman, was the military commander of Vicksburg after Grant left. Sherman and his men were encamped northeast of Bovina. Before he left Vicksburg, Grant ordered the old Vicksburg fortifications denuded and a new, shortened line built around the city. This house probably had to be demolished to clear the field of fire for these new fortifications, so it probably was Grant's order that destroyed the house. The story probably morphed into Sherman after he was demonized by the Lost Cause.