Cannabis is psychedelic to the extent that the term means anything. It's not a "classic" psychedelic like acid or shrooms, but there is no obvious category difference between microdosing shrooms vs. smoking a joint vs. having a proper trip vs. greening out, and so on. It's all spectrums of psychedelic experience caused directly by something you ingested.

The opposition to the term likely has more to do with proponents and lobbyists wanting to distance weed from the "harder" psychedelics that are known to fry people.