Edit: the study compared therapist outcomes to AI outcomes to placebo outcomes. Therapists in this field performed slightly better than placebo, which is pretty terrible. The AI outcomes performed much worse than placebo which is very terrible.
waitlist control, where people get nothing
psychoeducational, where people get some kind of educational content about mental health but not therapy
existing nonpsychological service, like physical checkups with a nurse
existing therapy, so not placebo but current treatment
pharmacological placebo, where they're given a placebo pill and told its psychiatric medication for their concern
A kind of "nerfed" version of the therapy, such as supportive therapy where the clinician just provides empathy etc but nothing else
How to interpret results depends on the control.
It's relevant to debates about general vs specific effects in therapy (rapport, empathy, fit) versus specific effects (effects due to specific techniques of a specific therapy).
Bruce Wampold has written a lot about types of controls although he has a hard nonspecific/general effects take on therapy.