Perfectly determining company data from personal data on a personal device is impossible. "We would never access your personal data" means "we would never access your personal data deliberately, only accidentally in the course of an investigation of your work-related activities". Obviously no company is ever going to sign an agreement promising to do something impossible like perfectly avoid inspecting any personal data during a device audit. The person from the story might as well have been asking for the moon.

If they make verbal assurances that they'll do nothing bad, perhaps they'd be willing to write them down on the contract.

The upstream comment says that not only did they refuse to back up their verbal assurance that "they'll do nothing bad" with anything in writing, they withdrew the job offer over it.

It's been some time since "Do no evil" meant anything there...