It may help if you had the source you originally found this in. This is a pretty spectacular claim, and its veracity could be checked more easily if there was a position to start from.

What was the text you used for that course? Does your college still offer it? If so, are they using the same text?

EDIT: u/Edicedi has found the text and the relevant passage below. My expertise is not in Roman History, so I don't have a good sense of the historiography around the study of Coliseum narratives. Hopefully now that we have the text someone with the appropriate background can comment on it.

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