Gulliver is kind of an every man's man. He's not too rich and not too poor. He's not a scrawny guy, but Gulliver also isn't a hulk of a man either. He's well educated, but not super intelligent. For example, he studied medicine at a university and served as an apprentice under a master surgeon, but Gulliver also never really engineered any of his escapes from danger. Normally, a hero character that is caught in a tight spot figures out some miraculous way to escape. That's just not the case with Gulliver. He seems more content to just wait out his situations instead of engineering them to his favor. Perhaps that makes him patient.
Gulliver is also a people watcher. He'd have a blast in a busy airport. I suppose that curiosity about people is what led him to go on his travels in the first place.
"My hours of leisure I spent [...] in observing the manners and dispositions of the people"
His genuine interest in other people allow Gulliver to easily adapt to the different cultures that he comes across in his travels. His propensity to pick up other languages also helps him to adapt quickly.