We simply don't say "learn driving" or "learn swimming". Consider that the word "how" is omitted (it is unnecessary).
I learned [how] to drive.
He learned [how] to swim.
Your understanding that "if you learned to drive, you already knew how to drive" is incorrect. When you take your first ever driving lesson, when you have no knowledge at all of how to drive, you have started to learn to drive. Hopefully, after 20 lessons or so, you will pass your driving test and become a qualified driver.
Retired English Teacher