I'm not 100% certain of how the medical/psychological community would define 'placebo', but I'd argue it's not as simple as this not being a placebo because it

I'm not 100% certain of how the medical/psychological community would define 'placebo', but I'd argue it's not as simple as this not being a placebo because it's an effective trick. The fact that placebos are effective is precisely /because/ they're effectively tricking whatever badly-understood connection there is between our thinking and our body. I imagine that there are degrees to this: 'tricking' ourselves to be productive by deciding to clean our house instead would generally not be called a placebo, whereas taking a sugar pill that lifts us out of depression probably would. But fundamentally they're just the same thing on a spectrum: an improvement as a result of something that we /know/ should not be effective by understood, biological pathways.