I think there’s plenty in ANH to show that it’s not a coincidence at all that Ben lives near Luke and has his father’s lightsaber:

“That’s what your uncle told you. He didn’t hold with your father’s ideals. Thought he should have stayed here and not gotten involved.”

“Your father wanted you to have this when you were old enough, but your uncle wouldn’t allow it. He feared you might follow old Obi-Wan on some damn fool idealistic crusade like your father did.”

Based on these quotes, I think it’s pretty easy to assume that Luke’s father was from Tatooine (in 1977, he was Owen’s brother after all), and while on Tatooine, met Ben and followed him on a crusade. It even implies Ben was originally from Tatooine, so it makes even more sense that he still lives there.