I'm intrigued by these sorts of studies - not coming from a statistical background I'm amazed by how few samples they need to draw conclusions. If you told me you only had 341 events in your A/B test I'd be suspicious of the results you were claiming. (Note: I don't do A/B tests professionally so I may not know what I'm talking about...)

They do mention " Random coefficient mixed models accounted for surgeon variability" in the summary so maybe that's sufficient.