"Fish", if taken as a monophyletic term, includes land mammals because tetrapods are osteichthyans -- bony fish.
In common use, "fish" is, however a paraphyletic group which excludes tetrapods but otherwise includes all other osteichthyans.
Since starfishes don't include tetrapods, nor vice versa (nor do they share biological features to be in a polyphyletic grouping like "crabs"), the relevant common term is "Animalia" -- "animal".
True. And all land vertebrates are technically fish.
They share a common ancestor with ancient fish, yes. Land mammals also share a common ancestor with starfish. That doesn't make them starfish.
The "humans are fish" idea comes from cladistics.
"Fish", if taken as a monophyletic term, includes land mammals because tetrapods are osteichthyans -- bony fish.
In common use, "fish" is, however a paraphyletic group which excludes tetrapods but otherwise includes all other osteichthyans.
Since starfishes don't include tetrapods, nor vice versa (nor do they share biological features to be in a polyphyletic grouping like "crabs"), the relevant common term is "Animalia" -- "animal".