How? He's an explorer. He's not a diplomat, he's not an ambassador. His job is exploring inside the Federation. He has difficulties with people getting his people killed.It's possible his behavior has changed dramatically due to the presence of his visitors, we've certainly seen that before with other captains. But the way others speak about him and the way he speaks about himself, gave me the impression that this is basically what he's like, and he's not someone who's up to the job of managing people and representing the Federation.
Despite his asshole nature he strikes me as reasonable.