If I'm not mistaken, they contractually limited manufacturers from selling devices with Android forks, according to Google to avoid experience fragmentation.

AFAIK the terms didn't limit any other operating systems not based on Android.

Yep actually I retact part of my original comment. Thanks for the correction.

The dumping part is still valid because any OS that isn't free and relies on licencing can't complete with an OS that makes it money from a secondary business like search and advertising.

Google gave away Android to make sure it dominated mobile advertising. Any OS reliying on profits directly from licencing the OS cannot complete.

Your comment is still false. Google allows Android forks with their services installed. You just can't break the API, which makes sense, otherwise apps from the store wouldn't reliably work.

No, the dumping part is valid. Free OS with free services to kill competition.

Wouldn't this line of thinking mean all open source code just dumping? The linux kernel, with lots of its development done by either volunteers or employees of companies who use it, is also given away for free. How can a paid licensed OS compete with what is essentially a co-op of developers across organizations giving the code away for free?

Is Firefox also dumping, since it's available for free, funded by donations and the default search provider?

This only becomes an issue when you are a monopoly as this is when it hurts the consumers ability to choose alternatives. If Android truely is the best option let the customer decide without trying to stifel competition.

Firefox and Linux don't work to stop competition in the same way. Neither care if manufactures provide other options or flavors and Linux especially has commercial forks like OSX and Android.

This is false. Samsung and others made Microsoft phones as long as it was a viable alternative. Google restricted others to prevent a split of their own platform - Android.