Agreed.
Seasteading is actually no different than sailing any old boat. The only difference is relative movement and time.
A person who sails across the ocean is seasteading all along the way – claiming exclusive ownership of a space. He is just changing the claim (a sequence of abondoning and homesteading new territory) faster than most other people do.
Depending on how you want to look at things, staking a claim on land is a form a “seasteading” through outer space because the Earth is moving around the Sun. There is nothing special about seasteading because you still have to defend your space from invaders.