According to a report from Android Police’s Artem Russakovskii, the review unit he sent was buggy in the sense that it basically recorded everything all the time, even when the “OK Google” hotword was not spoken. He discovered this when he checked “My Activity Portal” and found that the Mini was responding to dialogue spoken from his television.
So what caused this problem? Basically the touch panel on the top of the Home Mini was too sensitive, and that the fabric covering the device was enough to trigger it. This is one of the manual ways of triggering the Google Home Mini, similar to the Google Home. The good news is that the problem was caught early on before it was actually released.
Google has since pushed out an OTA update that disables manual activation completely, and they are also planning a long-term fix before the device is released to customers on the 19th of October.