In the past, did Goblin Slayer rescue Sword Maiden?
Goblin Slayer has been an active adventurer for 5 years at the beginning of the story. Sword Maiden defeated the Demon Lord with the Heroes and became gold-rank 10 years prior to the events of vol. 2. So, for Sword Maiden to be captured and then saved by Goblin Slayer, it would have happened way after she's famous as a gold-rank adventurer. I don't think it's been explicitly revealed WHEN was she captured, but I find it hard to believe it happened after defeating the Demon Lord, so the one who saved her was probably not Goblin Slayer.