This isn't unusual - maybe the quantum is (though I have no idea if "$7.6B worth of travel" is large or small in whatever context the article is trying to make), but airmiles are awarded now with the expectation that the airline must fulfill them later. Maybe 30k miles gets you a 1 way trip now, normally valued at $200. In the future, they could devalue the miles and a 1 way trip costs 35k miles.

Either way, they must be accounted for so yes it's normal to see this on a balance sheet. Is it alarming if you're an investor? Perhaps only if you think there will be a "run on miles" where nobody buys tickets suddenly and they all use miles to fly instead. But the airline will never allow that, plus these are all magic tokens any way, so not sure what the relevance of this in the article is.