why can prostate cancer recur locally if the prostate is removed with clear margins?

My father (68 years old, gleason 4+3, PSA 19.1) had radical prostatectomy (robot assisted) 10 days ago. The pathology report is all good -- negative margins, no tumor in the pelvic lymph nodes, no invasion of seminal vesicles. Right before the surgery, he also had a MRI and full body bone scan which didn't find anything outside of the prostate.

Today, we were shocked when the doctor said my father still has a 20-25% chance of having local recurrence in the next 10 years. Not "metastasize", but "local recurrence". My dad and I thought, if he has clear margins and removed the entire prostate, he's cured... how is the tumor going to recur when there is no prostate left??? I'm so puzzled.  Thanks for any advice.

(we know to monitor the PSA. yes we know prostate cancer is usually slow so even if it recurs, we can probably treat it successfully again. but still, we were shocked to hear it can recur locally..... what the heck? recur out of nowhere?)