It is not as much fighting in US as much as "fighting in a historically meaningful venue as the main event A-side for the first time in Japanese history following an absolutely dull and awful past two days and being essentially considered KO win or bust." Happened in Tokyo Dome, happened in T-Mobile, not sure about Riyadh as it depends on who else fights
Fighting at home matters. Time zones matter. His fights in Japan are usually on here (Australia) about 9-11pm. The fight in the US was about 1pm. Fighting outside of the time you usually do, or when you would usually be asleep is a recipe for disaster.
You see it in many other sports, there's usually an advantage to being at home, the travel, the unfamiliar environments etc. It can apply minor stresses that wouldn't be there when fighting at home which can effect performance. But any difference I think would have been very minor and I don't think we saw it visibly effect his performance as apart from one error in the 2nd round he fought a pretty flawless fight. He made the same mistake in a fight in Japan and got dropped too. So yes fighting overseas can impact performance but I don't think that was evident in the performance we saw from Inoue against Cardenas, because Inoue really wasn't extended that much and didn't have to really dig deep at all.