Old guys are eccentric.
Carrying a P-38 for CCW is eccentric, I don't care what anyone says.
Everyone over 75 has some degree of dementia.
He is probably lonely and/or wanted to talk about/show off his P-38.
A younger person probably wouldn't have done it or would have clued you and your buddy in better before doing it.
At least (besides drawing it unannounced in the first place) he handled it relatively safely.
You're right he could have started shooting, but then again anyone could.
"No free man shall ever be debarred the use of arms."- Thomas Jefferson