Every time you click on a link, your browser helpfully tells the website that the link goes to, where you come from.
Try clicking this link and see what it says :) https://www.whatismybrowser.com/detect/what-is-my-referrer/
Try clicking this link and see what it says :) https://www.whatismybrowser.com/detect/what-is-my-referrer/
Keyword being "a little". It's a cookie set on previous visit.
$ document.cookie
> HN=1