While not technically a precise loading indicator, this seems to be along the lines of giving a better user experience than anything else. Gmail has real dark patterns though. One of which is to load the emails first, and then after a short delay (even on a fast connection) load advertisement rows on top. So if you attempt to click one of the new emails on top, you're just as likely to hit an ad that just loaded in that space.

Probably creates a ton of false clicks for whoever is paying for that advert.