How can DSA functions be used without extension names on lower versions of OpenGL?
How is this possible?


Because ARB_direct_state_access is an extension. Note that the function/enumerator names in that extension lack the ARB suffix. There are dozens of ARB extensions that work like that. Suffix-less extensions were introduced in OpenGL 3.0 for compatibility purposes. You could write code that could work on OpenGL 3.0 or extensions that expose 3.0 functionality, without having to write different function calls.

The same goes here. You're not using OpenGL 4.5; you're using OpenGL 4.4+some extensions.