Photoshop's content-aware fill first appeared as a third-party open-source plugin for the GIMP.
While one certainly can't equate the two I have found GIMP works well for a broad array of digital imagery tasks... just like Photoshop.
Much of Photoshop's dominance has to do with the network effects of Adobe's ubiquitous ecosystem as much as the comprehensiveness of their tooling.
Indeed it did, and that plugin was hard to configure and hard to use. I remember installing GIMP just to try that plugin out, and it was not fun, it involved a lot of manual steps to get it working, and I never quite got the hang of it.
In contrast, when I got my hands on a version of PS that supported content aware fill, (which admittedly ships in the box, skipping the installation step) I was able to figure it out in a few minutes and start getting good results in half an hour. I am pretty sure I spent more than half an hour trying to get the GIMP plugin installed.