He said Shanks CAPTURED Loki, thats literally all he said. He didn't stated he tried, and he also didn't stated who else tried. You literally just have a 100% confirmation that Shanks and some unknows actually tried, while Shanks managed to do it.
Why would a Gaban out of his prime, with a child and a wife, give his all fighting Loki? While Loki is already friends with the main protagonists and we barely know his past and actual evil deeds.
I feel like this is another "It's not Gaban, its Shiki" level of guess