Seems like Jackson has a bit of misunderstanding...he refers to close as in birth year, but Sohyun refers close as literally close relationship... Thats why he said we're close (same age) and Sohyun said no, we're not close (relationship), hahaha!
I think he is overly excited whenever he met up with friends of similar age, and starts quarreling with them^^
But the good point is, Jackson makes Sohyun glows a lot in this show. Now i will always ESPECIALLY notice her presence in any shows she attends.