Again it’s not a misstep, just because they’re isolationist doesn’t mean they’re not keeping an eye out on what’s going on in the world and it’s known that the king has gone outside of the borders and like any dignitary would bring something back to show the rest of the team back home. Young T’Challa was may have been flipping channels on the satellite and may have come across Robin Hood Men In Tights, who knows but we do know that mixed in with that and his desire to explore beyond Wakanda. Which helped shape this T’Challa who after being told that Wakanda was destroyed he didn’t want anyone else to go through the loss he was going through hence the bringing families together and finding ways to save planets.
Except this T’Challa didn’t grow up in Wakanda he grew up in space so he kept the few things he learned from T’Chaka and mixed it with other things he admired as a pre-teen/teen kid, all he had physically left of Wakanda was literally his Panther chain. Which as he thought he was the last Wakandan alive that even The Collector thought as well he talked down Thanos, saved countless lives, was still a master strategist, was still humble and tried to get Thanos and Nebula into counseling while also clapping them blue cheeks.
Hell this T’Challa did more in thirty odd minutes than comic runs by McGregor/Thomas/Coates and wasn’t a sad sack or punching bag