Seems pretty common sense to me that you're gonna have more people with hidden cancers coming in to get CT for phantom pains, etc and later discover they had cancer all along. That doesn't mean CT caused it. Did the study control for this?
No, because that's not how the study worked, i.e. it wasn't actually tallying cancer rates from people who had CTs. It basically just looked at the amount of radiation that a CT scan gives a person, and then extrapolated the cancer that would be expected from that radiation dose based on other data we have of e.g. people exposed to radiation in their jobs, and nuclear fallout occurrences.