Responses
It was explained that it happened at different time for the both of them; Seojun thought that he was just clearing a quest, but he most certainly traveled between dimension and time as he should be, to meet Erszebet. Prolly the reason why she wasn't able to introduce herself earlier but after the tutorial dungeon.
He met erszebet in that tower at greece AFTER his regression. that means he never met the witch before his regression? But erszebet seems like to know him? Like what happen i don't