This issue simply occurred because a small number of Mini's given out at a Google event had a defect where the "press to send voice command" registered phantom touches.
Not only was this clearly unintentional, but the issue was "resolved" (not really because they just disabled the would-be feature) and deleted the data they accidentally collected in a few days. Very few people were impacted.
It was an over sensitive capacitive touch sensor. I can understand the scepticism but if you've ever tried to make one you'd understand it's easy to screw up in subtle ways that only repro on a subset of devices.
[0] Google is nerfing all Home Minis because mine spied on everything I said - https://news.ycombinator.com/item?id=15446206