It's hard to know what it isn't for certain but there are many other reasons papers list contributors in a flat structure (be it random or alphabetical order). Particularly with large numbers of collaborators.

"References" section sort of narrows the field anyway.

As someone whose last name is near the end of the alphabet, that's not the first presumption I had seeing that page.

Not very hard to look people up on LinkedIn and figure out who the core researchers are. I think this is just a very surface-level overview paper that encompasses a bunch of different research projects conducted by different teams, and it would be difficult to order the contributors in any meaningful way.

Well meta already got Ruoming so he can obviously give them a ranked list of who to grab.

Most of his team are former Google brain so GDM knows who is good.

Considering a large portion of the contributors have names originating in a script and language that has no relationship whatsoever to English’s already arbitrary letter ordering, this list configuration is as good as any.