The engineers on the proposal are all google employees and the presentation is consistent with proposals made as if speaking for their employers. It's not exactly common but it happens that proposals like this are made on the proposing employee's account, as google is so unfathomably large that many employees may not have push access to Google repos. However, given that this is a rather large and controversial proposal, I'd wager that this was a political decision to not "taint" official Google repos with this, enabling them to say "well it's not a proposal by Google the company we actually love our users :)"