The biggest thing he did wrong was not having a 180 lb Alsatian to EAT a trespasser, or landmines to blow a leg off during the retreat, or SOMETHING to make the would-be burglar the next morning's headlines, with photos showing the coroner putting several bags in the wagon. He grew up and lived in a different time when it was a lot easier to trust people because there used to be consequences for the untrustworthy.
Dirtbags abound. Pity it's illegal to shoot folks that deserve it. "He needed killin' anyway" used to be a valid defense in Alabama. Whoever did this knew he was hearing impaired, I'd almost bet on it, and probably someone that he's talked to at some point in his life. I'll also wager their life ain't worth spit if he gets to them before the cops do.
Hopefully he had the serial numbers on the guns and if one pops in a pawn shop, there will be video to go with it. Hope LEO's catch the scum and he's stupid enough to point a stolen weapon at them. All it will take is ONE unique weapon get an idiot caught. If they're not complete idiots, though, they'll dump the rare stuff in the river so they don't get caught with it.
There's no describing that feeling of violation to be robbed that way. Since he was in the home, and since firearms at some point were in the possession of the robbers, it became armed robbery, not burglary. At least that's the way it works in Alabama. Hope the law is similar in Maine. Makes it a lot easier to get air-wasters off the street that way.
Seriously, the old fella really needs to consider some kind of security measures, especially with his hearing impairment. I know he wants to trust everyone, but I think it's just been proven that not everyone can be trusted.