Nah, happens quite often when Google refuses to serve the results you're asking for (ignoring a keyword, using something it believes is a synonym but is actually not in this context etc.), and one therefore do many successive almost identical searches with small tweaks.

I wasn't behind CGNAT. Had a dedicated public ipv4 ip. I was just using google a lot, sometimes.

Google does bot detection on a /24 basis. So you were still sharing with 253 other households most likely.

That would be idiotic. I don't think Googlers are idiots.

Of course they're not idiots. They're googlers, which means they have a very specific worldview and a work environment that focuses their perception of the universe into a very specific way of looking at things, where "scale" is both the cause and solution to all problems and of course attackers use whole subnets at a time and need to be shadowbanned appropriately.