If you read the first page, Ichikawa thought at first Yamada was just teasing him or was simply another one of those "small talk" moments. Only then with the combined circumstances later that it dawned upon him that she's using a pick-up line and was indeed trying to pick up his LINE earlier. His AH! moment also accidentally served as (an apparent "Jelly Block!") mechanism to interrupt Yamada. Still, despite the recent epiphany, I bet our dense edgy boy still doesn't have a clue as to WHY exactly she wanted his LINE, or could be still in denial.