Interesting to compare the coloring to an earlier version:

I interpret it as bullethead being a highly-skilled artisan that used ketchup (or similar substance) to create art. Ketchuphead thinks he can recreate the art but is missing the skill to do so and just has the raw materials.
My diet is pretty SAD. It's probably higher quality than average, since I'll avoid the cheapest possible foods that are chock full of artificial this or that, but it's still not as good as eating real food.
This is an older look at some of the foundational work that went into today's LLMs. It links to a tool that you can use to explore the associations:
https://lamyiowce.github.io/word2viz/
I think it's hard to say that language models don't "know" things based on even older results like this, even if they "know" things in a completely different way than humans do.
It's a pun on desert/dessert. At first you think they're in a desert and the character pronounced it wrong/author spelled it wrong, but the final panel reveals that it was accurate and they're on top of a large dessert, which is possibly also a desert as well
That's great! Did you make it yourself?
It's been borrowed into graphic design as the Cicada Principle:
https://lea.verou.me/blog/2020/07/the-cicada-principle-revisited-with-css-variables/
Looks like the original link is dead, but there's a newer examination of it. If you have a repeating pattern, you can maximize variation while minimizing file size by using multiple sequences with different prime lengths
He's being abducted by a UFO and wakes up inside of it to see random teens instead of aliens, is the joke as far as I can tell. I found the last panel online used elsewhere but it seems to be a common stock photo and not a meme or reference on its own.
Man, Google AI is the gift that keeps on giving (stupidity)

There's no list that I know of, I had to go trawl through archive.org to find everything. Not really sure why it got taken down, other than that the author has said in interviews that he's kind of a perfectionist and enjoys scrapping art that he's already done if he thinks it isn't good enough.
You can kind of see that with my other comment with the older version of this strip. He redid it at least once to add some subtle coloring to draw the viewer's eye towards the background where they see the vulture and get the joke. Probably just a lot of that sort of thing.