sshhhhhh, its a dream, dont try to make sense of it
no but actually, this dream sequence takes place before kihoon and yeon meet again in season one, so between when kihoon graduated middle school and yeon enrolled in college. it takes place literally RIGHT before, so im pretty sure yeon has started his first semester, hes 20 and kihoon is 21, and then they run into each other. throughout all of season 1 we see that kihoon gets flashbacks of their previous life together, so it makes sense that in his dream the past life version of yeon also shows up. he usually gets the flashbacks as dreams, so when hes dreaming he clearly remembers its his past life, but when he wakes up its all fuzzy. i hope this helps!

i’m a tad bit confused as to what’s happening