Easter egg: On the 2nd disc go to storyboards. Go to the 2nd page and select rhino fight under Deleted Sequences. Press up once to select the rhino and press enter. This will get you to a section called What Happened to the Rhino.
Easter egg: On the 2nd disc select trailers and TV spots. When you are in this press left once, this will highlight the bird on his chestplate. Press enter and you will get a funny Chicken Run trailer.
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 ★