King of Tokyo: Damage dealt on first entry in to Tokyo
Damage rolled outside of Tokyo is dealt to those in Tokyo.

Each [Claw] results in a point of damage dealt to Monsters who are not in the same place as you.

If you are in Tokyo (Tokyo City or Tokyo Bay) when you get [Claw], you deal damage to all the Monsters who are not in Tokyo.

If you are outside Tokyo when you get [Claw], you deal damage to
all the Monsters who are in Tokyo (Tokyo City or Tokyo Bay).



Note that it's your location when you get the Claw result that counts, so your location before any moves. There's nothing to support dealing Claw dice damage to those in the same zone as you started.
The passage you quoted simply reminds you of the above. It also instructs you that dealing damage to noone is not dealing damage at all, which may matter for some Item cards.