The reasoning behind having real people snooping on recordings is to improve the voice-controlled assistants' performance and command recognition, of course, nothing nefarious, but having access to personal and what most people would assume, confidential, conversations, is a big no-no.
That wouldn't even be such a problem if the Siri activations were done with the respective phrase, yet sometimes your HomePod or Apple Watch mistake other phrases for "Hey, Siri!," and even a zipper sound has happened to send a request or two on an occasion. Apple's response is in line with the "nothing nefarious" train of thought, of course:
Still, if you don't want some unknown researcher snooping on accidental Siri recordings, there is a way around Apple's existent automatic system for opting you in. Here's what you need to do:
1. Go to Jan Kaiser's GitHub repo and click or tap on the "Prevent server-side logging of Siri commands.mobileconfig" file link
2. Switch to "Raw" view from the buttons above the code to download the profile on your iPhone or iPad;
3. Go to Settings, and click on the first "Profile Downloaded" option at the top;
4. In the profile screen, tap on the Install option, then tap Install again after the "not signed" warning;
5. That's it, you have now opted out of accidental Siri recording reviews by third-party contractors, neat!