But different doesn't mean random. An attacker could test every possibility for that pixel rather quickly. Even faster if you know a bunch of the pixels are, for example, a shade of gray.

I found an explanation where they bring up the issues I brought up as well as some others.

https://blog.cloudflare.com/lavarand-in-production-the-nitty-gritty-technical-details/

They give an example with one red value for a single pixel. They don't address my point that there are a lot of pixels like that one, maybe not all would be 50/50 like their example but a lot of pixels would have a much narrower range of values than randomness.

But they answer my second point about a hacker putting something in front of the camera with known values and that answer sort of takes care of everything. It boils down to, it doesn't matter because the lava lamp wall output is mixed with other sources that an attacker doesn't have access to.