Experimental groups are often called treatment groups or treatments even when you’re doing a toxicity test in insects or something else decidedly not medical

I'm not from the field but I think anything done to a patient, effective or not, is technically a treatment. From everyday life: you can give someone the silent treatment, or treat them like a baby, or what have you. Anything that isn't the default thing you'd do anyway is a treatment. So in medicine I could believe that anything at all that a doctor tells you to do, or does to you, is treatment.

And it would make sense in a controlled trial that "the treatment" would refer to the treatment being tested. It's a treatment for sure, we just want to find out if it does anything useful!

Not if your blinded I guess. But there is a treatment group. Look up treatment - doesn't mean it's effective, it's just a process or something that affects something else. I'm calling it trick or treatment from here on in.