Open it and copy the whole contents to the clipboard
Go to the empty elisp file and paste the text into it
the example file contains a huge lisp expression with an indentation error in it, so when you paste it into a lisp buffer with aggressive indent on, aggressive indent corrects the indentation which is good
you are at the end of the expression, press C-M-b that is backward-sexp
You get the "Unbalanced parentheses" error though the expression is balanced. You can check it by going to the beginning of the file and pressing C-M-f. If you step into the vector that is at the end before ] character and keep pressing C-M-b, you can find the problematic point. There the syntax highlight is mixed up. This only happens with aggressive indent on.
There is a discussion of the a problem on Emacs help:
https://lists.gnu.org/archive/html/help-gnu-emacs/2022-01/msg00148.html
Turns out the problem can only be replicated when aggressive indent is on.
Steps:
Tested with Emacs 27.1