That's not accurate, and you're misinterpreting the info from the white paper. They're stored during the original period with a RANDOM identifier, and then later, without any identifier. That random identifier can be reset by turning Siri off and on again, which deletes all of the Siri info tied to it. It's not tied to an Apple ID. I'll make that clearer in the article.
"When Siri is turned on, the device creates random identifiers for use with the voice recognition and Siri servers. These identifiers are used only within Siri and are utilized to improve the service. If Siri is subsequently turned off, the device will generate a new random identifier to be used if Siri is turned back on."
"User voice recordings are saved for a six-month period so that the recognition system can utilize them to better understand the user’s voice. After six months, another copy is saved, without its identifier, for use by Apple in improving
and developing Siri for up to two years. A small subset of recordings, transcripts, and associated data without identifiers may continue to be used
by Apple for ongoing improvement and quality assurance of Siri beyond two years. Additionally, some recordings that reference music, sports teams and players, and businesses or points of interest are similarly saved for purposes
of improving Siri."
The white paper:
https://www.apple.com/business/site/docs/iOS_Security_Guide.pdf