Apple’s press release specifically notes that the training lines are randomized. You’d need to get 15 minutes of audio of the person saying the exact lines that the training asks for. Doesn’t seem like a huge risk.
I doubt if majority of people would sit down to say "The pleasure of Busby's company is what I most enjoy. He put a tack on Miss Yancy's chair, when she called him a horrible boy." to even try out this feature