Earlier quoted context omitted.
I think they expect people to fly less; similar to many other “sin” taxes like those on alcohol or tobacco.
I'd argue it's a bit of both -- it's a sin tax, and a pigovian tax. Sin taxes _are_ meant to cut down on use, while pigovian taxes aren't meant to cut down on use, rather, make up for external damage (such as to the environment). https://en.wikipedia.org/wiki/Pigovian_tax
And if you're contending they're different I assume one is supposed to cut down use.