Not a DAK trigger.
I re-examined the trigger bar. Nothing unusual. Spring looked fine, and no sign of a burr that had been worn off.
Who knows. Ill advised attempt to pry trigger bar out, slip of a screw driver screwing around with the spring, or maybe some weird maniacal grip removal technique?
After a good night's sleep and looking at it this morning, I'm comfortable that it wasn't due to any normal operation or function of the 229.
End result. Function checks fine. It's now back with the customer. They weren't eager to discuss where the damage may have come from since some colleagues were in at the same time.
I'm left with a mystery but will definitely be on the lookout for anything similar in the future.