https://imgur.com/a/1PJ3FHh
Why there is another factory? How can I go there, or use it?

Factorissimo uses only 100 surfaces (dimensions) for all its factory building interiors. Once you have more than 100 factory buildings, Factorissimo will start reusing surfaces evenly. That is why you will see other factory building interiors on the same surface. In this case this Mk1 floor must be one of your earlier factory buildings, probably one of the first few you ever built. Don't worry, everything will still work fine.

My question is why don't they automatically light up as though they're Radar'd :P I'm also trying to work out a way to cheat and send stuff between them without the need for exporting and importing from factories but you've done a great job keeping them far enough apart to prevent that