Fax isn't encrypted. If you wiretap the line, you can just read off any faxes. Email can be sent over TLS, and the email itself can be encrypted with PGP.

However, superficially, fax is more secure because there are no stored copies (maybe depending on the machine?). There's the original, and the copy that gets printed out on the other end. If you were to fax over a script for a movie, there wouldn't be a copy sitting on a disk on the receiving end, there would only be a printout. That's what Ridley Scott is alluding to in that video.