Bernard was part of the Tailies because he was in the bathroom when the turbulence started, Cindy the flight attendant informed the passengers to buckle up because of the turbulence. As Bernard was making his way back to his seat the plane jolted again really bad and he decided to buckle up in the nearest seat as would anyone do when someone experiences that much turbulence. It is basic human instinct to protect oneself when facing great danger and the only way he was able to protect himself was strapping into the nearest seat available.
Bernard wasn't a casualty of death or being captured by the Others because he was not supposed to be with the Tailies.
This makes sense, the only prominent/semi-prominent characters in the tail section are either dead or weren't supposed to be in the tail section.
He learned his skill from hunting for sport, as proof Rose says;
ROSE: Bernard, this is not pheasant hunting in Montgomery County. ("Greatest Hits")
Served time in the military, where he acquired his skills as an expert rifle shot.
The reason why he's not a "good person" and wasn't on Goodwin's list.