It's common to distinguish between "psychedelics", which primarily function via serotonin receptors, and "dissociatives", which primarily function via NMDA receptors.
The term psychedelic is describing specific subjective effects rather than a mechanism of action, what you're thinking of are the classic serotonergic psychedelics which are 5ht2a agonists but ketamine and other dissociatives can be considered dissociative psychedelics
