You’ll remember Luke harping on “the legend of Luke Skywalker”

Well, Kylo fought the legend, not a literal projection of present day, old, washed Luke. Kylo would’ve smoked actual old man Luke, but the Legend Luke was an exaggeration of even the Luke we all know from the original trilogy - doing back bends, eating those missile blasts, he was a tall tale come to life before everyone’s eyes (kind of)

That’s what I think is so slick about that part, that he’s portraying the hero Luke that everyone has in their head, the Luke that Kylo Ren is still intimidated by.