I didn’t find it confusing.
I was never confused by that line.
I think you guys are underestimating how confused newcomers are to the series when that line is spoken. At this point in the franchise, we only know of one Skywalker: Luke.
Unless for some bizarre reason a person has skipped Star Wars and gone straight to The Empire Strikes Back they would have heard and known:
LUKE: How did my father die?
BEN: A young Jedi named Darth Vader, who was a pupil of mine until he turned to evil, helped the Empire hunt down and destroy the Jedi Knights. He betrayed and murdered your father. Now the Jedi are all but extinct. Vader was seduced by the dark side of the Force.
Now, I don’t know where you’re from but it’s pretty standard for children to take the last name of their father. So yes, we have heard of another Skywalker before ESB.