Again, not necessarily. Different things cause different cancers. You're unlikely to get melanoma from smoking; you're unlikely to get liver cancer from a sunburn.

CTs may not cause significant amounts of wrist/knee cancer - I can't speak either way on that - but that wouldn't mean they're 100% safe elsewhere. For starters, wrist/knee imaging needs less radiation - they're relatively thin parts of the body, and relatively small regions.

But then the assumptions behind the article is not general, and the conclusions would have to amended to the radiation dosis and/or tissue. Which makes sense, of course.