AAIB do not speculate on the two crew issue so we have to assume they give it no relevance.
Or that they have insufficient data to base their speculation on?
In all honesty who could predict that a faulty bearing in an ACM could lead to two engines being shut down...
In a way, Cessna has predicted this by not supplying any memory items/drills to be performed in case of (suspected) engine vibration. They want the pilot(s) to analyse the problem first according to the checklist before shutting anything down.
Like "Pilot A", I have flown piston twins for a long time before moving to the Citation (he had flown the Pa31 in the five or so years before getting type-rated on the Citation). With a piston twin, flying low and slow as they did, your only chance to get out of trouble is to shut down / feathering the malfunctioning engine as quickly as possible. Especially with some Pipers where a locking pin prevents the propeller from feathering once the RPM has dropped below a certain figure. Maybe this explains the haste with which the engine(s) was/were shut down? Without a voice recording, we will never know.