Economists certainly know this, as would many historians.
"people should stop training radiologists now" – Hinton, 2016
But they are being used by radiologists, not instead of radiologists. And because scans can be interpreted more quickly and cheaply, more scans are ordered, which has increased the demand for radiologists overall.
This is the kind of process that happens with any new technology. Hinton probably just didn't know because he's never worked outside of academia. A common problem with people commenting about "the future of work", AI-related or otherwise.