That's not a new word, perhaps just resurfaced. I grew up in the OC in the 80's and we used Chill then.
Hey bro, that game is pretty chill.
I just saw this movie, it was chill man.
It was a chill session at Brook St. this morning.
It is a stoner surfer driven slang that dates back a few decades now. Not that I was a stoner surfer as a teenager growing up on the beach in so cal or anything....