Yes exactly. It's an exaggerated version of the common "pressure signs" people see in rifles as well, that are often due to headspace. In this case, headspace can be measured in fractions of an inch rather than thousandths.
Try measuring case head expansion on a case that does this...
Notice the missing chunk of rim too where the extractor was - that wasn't ripped off from extraction, it was sheared off in the other direction when the case slammed back past the extractor.
