The difference between a fontset that looks similar and a fontset that solves for all the business requirements can be vast. Cereal appears to be extremely versatile and distinct in a few key areas. You don't need a custom font to distinguish your brand from others, but you probably do if you're going to be using that one typeface for every damn thing in every damn scenario.
I think the fact that this new font has an installed base of 0 counts against it's versatility.
I think the fact that a negligible amount of the general public could pick the new font (knowingly, not by guessing) out of a group of 9 other sans fonts counts against it's ability to distinguish the airbnb brand from others.
I don't think more than 1 in 9 people chosen randomly out of the general public would be able to accurately name any font and don't think this has any bearing on distinction. I did ask a followup question regarding the similarity to Netflix Sans however. Secondly, I don't understand your first statement.
The installation process isn't the sum total of the point there. Known-good is better than unknown, all other things equal (and not to sound condescending but they basically are).
It's low risk but frankly it's even lower reward. If their goal was to distinguish themselves, perhaps they could do it more effectively through something people would notice.
The font looks almost identical to a lot of other sans fonts.