Seems like this study set people up to believe a system was trying to help them so instead of seeing a random set of events unfolding they were looking for a pattern and then trying to attribute that pattern to the system they believed was helping them.

This doesn't seem like the placebo effect, it seems like an example of the human mind trying to find patterns that don't exist. Just like when someone tells you a cloud looks like something and then you can't stop seeing that thing in the clouds until it goes away. Tell people there's an AI and they can't stop seeing it, even if it's not there.