What are the rules/range for chunk loading in single player?

Solution 1:

The generation of chunks can be affected by other things than just players.

If you have a generated block that may or may not affect something that's happening in another non-generated chunk, the chunk is loaded, so that we prevent something like a Schrödinger's cat situation.

In your case, there's a redstone signal coming out of your solid block at the edge of every chunk, so the next chunk is loaded - and what a surprise! There is a block that can receive the redstone signal, which passes it on, and on...

To add some evidence, I did a bit of testing. I ran a command that tests for a block at certain coordinates:

/execute if block <x> <y> <z> [block]

When the redstone signal wasn't on the output was as following:

That position is not loaded

When I turned on the redstone signal, though, it suddenly worked.

Too bad I cannot think of a solution to your previous question that would work more than once and without having to be reset.

And even though this is something that might seem pretty obvious, but is worth mentioning: This doesn't occur for redstone only. Hoppers, Droppers, Observers, and many more blocks do the same.