Lundberg name

Hello - I have family from Sor-Trondelag who lived on Roden and Halstad farms. When they came to America they used the name Lundberg. I am a bit confused why they would take this name. Might anyone be able to clarify this for me? My ancestor was Randi Lundberg (Mjoen), and her brother was Ole Halstad. Their parents were Ole Pedersen from Auren (Øien) Farm, North Trondelag, and Beret Rasmusdatter from Tønset Parish, Hedmark County. Thank you.