More info on this? Unless I'm misunderstanding something, in my own test, this isn't true. You can hit loops, e.g. the page for Russia goes to Eastern Europe which goes back to Russia.
At "Branches of science" it links back to "Formal science".
Keep in mind, you need to click on "first non-parenthesized, non-italicized link" in the article text itself.
EDIT: I suppose one disproof would be the existence of articles that don't have a second link.
Stems from https://xkcd.com/903/ alt-text. Might not be the original source, but that's where I know it from.