The phrase:
"Why would a surgeon know anything about anesthesia risk?"
could be misleading to someone who has never undergone (or just didn't understand) what a pre-surgery anesthesiologist consult is for.
Surgeries are performed by teams. Anesthesia is one aspect of the procedure and most of the doctors know some, while surgeons know a great deal. The anesthesiologist's job, as a physician, is to monitor, adjust, and assess risk during the procedure. This disclosure, if it happened, was during the consultation.
Idunno, maybe because their entire career is performing surgeries which include anaesthesia and they have worked for potentially decades alongside anaesthesiologists? For instance, I've worked in the same type of role (programmer) for my entire career and I somehow know a ton about the disciplines adjacent or closely related to mine, especially because I work with them every day.