Yup. Flag removal worked.
Yes, you were very lucky with your grandfather and his record keeping. I sort of think there doesn't have to BE a "why". At that time just about everybody in Sweden were adopting surnames. Well, not everybody - a lot of people also kept their -son names. But the were many, many who took names of the Lundström - Lindquist - Nordgren - Högberg - Ekeblad et cetera type. Just a sign of the urbanization. With the old patronymic names you more or less had to know which village Anders Persson came from to be able to know which one of the five Anders Perssons in the parish you were talking about. The towns were just too big units for this to work.