Character mistake: When Maximus is talking to Marcus Aerelius, he mentions that his wife has black hair. But in the scenes where we see her, she actually has brown hair. (00:24:40)
Character mistake: Prior to the opening battle, Quintus says "The danger to the calvary" instead of "cavalry." (00:04:00)
Chosen answer: You're probably closest with the suggestion that they're rather stunned at the sheer speed with which Maximus has carved through the opposition. They'd certainly be used to more of a show, so for Maximus to slay all his challengers in less than a minute would take them aback. If anything, the "Are you not entertained" is closer to the theatrics that they'd really expect to see, which would prompt them into cheering him - up to that point, he's not exactly won their favour, even though he's defeated all comers.
Tailkinker ★