Lightroom and other professional-level are touted as being "non-destructive". Is PhD also non-destructive?

I am not sure whether any time I open an image file and manipulate it ("edit" it, maybe by flipping the image over or something like that) in any photo editor which is NOT "non-destructive" I am actually somehow destroying the file.
doesn't a "destruction" happen only until I decide to save/export the image file? does actually making any change while open in the editor change the file itself? Isn't what we see in an editor only a rendering of what is kept in the RAM, but not the actual file in the hard disk? If this is the case, why would it suffer any destruction?

Thank you