The shitpost is correct. Bony fish, or the superclass Osteichtyes, absolutely is a scientific classification, and by the way modern cladistics work, every single thing descended from them, which includes all terrestrial mammals, reptiles etc. are also bony fish.

In other words, if the common ancestor of tuna and squirrels and whales is a bony fish, they are all bony fish. The squirrel and whale cannot be demoted from their bony fish status.