You fight the fight with what you have at the time.
The .380 is probably nicely concealable and fits his hand well.
And, it’s what he had...
I'm sure gentleman who fought back will be upgrading the caliber of his weapon shortly.
I think what would be fun to do is convert a Glock to .50 GI.
You can get the conversion for about $600 from
this company for the Glock 20/21.
More on the .50 GI round
here.