ON4UN Low Band DX'ing Question: How can a non-terminated beverage be unidirectional?

I was looking at the designs for a reversible unidirectional beverage antenna in the book Low Band DX'ing as I have a spool of RG-6 that I thought I would make a BOG with. The part I can't get my head around in these designs is how they can be unidirectional without a terminating resistor. Can anyone explain this to me?

https://preview.redd.it/sissyw0qgcvd1.png?width=366&format=png&auto=webp&s=3443f10c727d6cfb08d4916c4cd9b5f98a959443