You shouldn't be surprised @TheWalrusStoletheShow .
The way they screen for prostate issues is first of all a blood test (PSA) then an ultrasound probe if the PSA is high (and they can tell a lot from that.)
Then if it's suspicious they will take a biopsy. If the biopsy is clear, then they won't go ahead doing MRIs etc. Obviously with KC, the biopsy was clear.
What they have said is that when he was having his surgery, something else was found(by chance (perhaps in the bowel or bladder area?) even though his prostate was benign. There are many ways of doing the op he had and they can use cameras, ultrasound and robotic surgery.
OR it could have been some markers in his blood or urine that alerted them to something else.
I'm of an age when I know men who have benign prostate issues, some have had all of these tests and some, which is how I know the process, and some sadly, have got cancer.