It's the API itself, it's a little more complicated than just checking if you have a chromium browser. What it's looking for is special tokens generated by google within chromium browsers. Google is selling this idea as a way to help verify identity of the end user and thus block bots. That's concerning, because it suggests that google will have some verification method likely involving ID and generate a unique token with that info associated with it. This is a real concern for web privacy for like a million reasons, obviously, and ideally should not be adopted by anyone. If other tech gatekeepers adopt it (and they would love to) it will block giant swathes of the internet from people refusing to use the tech and further googles monopoly over general consumer browser use. Now, could the token be fudged? Possibly. But it will take time to figure out.