@Korvalus Well, I checked the first chapter of the main story and he already has 'Singleminded pursuit', which basically boosts his growth 'cause he's in love with Ais. Both Bell and Hestia are shocked by his stat growth already. And in chapter 47, he ranks up and gets his new skill, 'Argonaut'. BTW, 'Argonaut' just lets him store power to charge up attacks.
So, his growth was there from the start, but I remember people being really impressed when he fought a minotaur
before ranking up. They were remembering the story of Argonaut during the fight. So, he probably got the skill because of them. IIRC they were also shocked when he showed the power of 'Argonaut'. So you're partly correct!😄
'Argonaut' didn't cause his growth, but it did draw attention to it.
Edit: Also, only Hestia knows of 'Singleminded pursuit', his starting skill.