When critics and hypertext authors say that the text is non-linear, they mean that the reader has a choice of paths through the text.
But of course, a reader can only ever choose one path at a time. So the text is linear, but not merely linear. I prefer to call such texts multi-linear.
The multiple paths mean that the hypertext author has to allow for reader choices.
In a printed book; the reader has a choice of pages, but most begin with page one, and turn the pages in sequence. For narratives, this is the only way to read (leaving aside "Choose-Your-Own-Adventure" books).
For poetry, individual poems will almost always be read line-by-line.
In hypertext, the choices make the meaning.