One of the best things about words is how they can mean completely different things depending on who is saying them.
Slang and pidgin dialects aren’t misuse either — they’re how languages evolve.
When I was a kid, swag meant several varieties of crap.
As in, “those sneakers are swag (ugly)” or “maths is swag” (boring) or “Mr Linnane is swag” (he’s a prick).
In the couple of decades since (or maybe it always was), swag has come to mean the clothes and trinkets that brands give out, enthusiastically festooned with their logos, as if they were automatically cool.
This swag is typically worn inside the office or while redecorating the house but rarely anywhere else, primarily because it’s got some company’s logo all over it.
If the gear was intended to serve the wearer, the logo would be discreet: Here’s a nice gift you want to wear.
But it’s not.
It’s covered in a brand logo to serve the brand.
And that’s what makes it swag.