How does file's More Info attribute work, and how to access it from a terminal? I want to understand where parameters like More Info and Comments are really stored (is it hfs filesystem specific?) and how to access this type of information from terminal.

"Who" updates this More Info parameter when I download some file from some website ?Chrome knows about it, or MacOS ?
If you're looking for the metadata this blog post has a helpful description of what you can pull from terminal and which utilities to use to access it.

Edit:

Just to future-proof this answer, the gist of that article is:


  To see these details in-depth, you will need to use the Terminal’s
  mdls command, which will list all the metadata tags and values bound
  to a specific file:
  
  
  Open the Terminal.
  Type mdls followed by a single space.
  Drag the desired file from the Finder to the Terminal window, or otherwise target the file using Unix file path syntax.
  Press Enter to run the command on the file.