she literally says she has no idea what it means and obviously she doesn't because it's just some thing his family talks about and she even said she doesn't.
I'm sure we're supposed to read it as this is them supposed to end up together but there's no actual reason for this to mean anything other than jumping across some rocks with her childhood friend for kiyo. But considering the mangaka must love kenta from spending most of the last several years just writing about him obviously the former protagonist will end up with the new protagonist.
In reality, the author just did a speedrun to finish Kenta's character arc by the end of the manga, because she couldn't find the time for it before for one reason or another. But let's not repeat ourselves. I agree that trying to reduce it to Kenta x Kiyo is really weird, since two thirds of the story was about how hard Suu crushing on him, while Kiyo was in a perpetual nakama power phase. Hell, Kenta and Suu even blushed each other in the last chapter. It's like Aiko-sensei didn't have enough time to finish this subplot as perfectly as possible after all. Because I have a vague feeling that 2 or 3 extra chapters could somehow fix this, at least partially.