This was found on another person's laptop who helped found Otto though.

If enough engineers leave company A and join company B and all are working in the same field, I would expect at least some of those employees to have documents from their previous employer, even if only accidentally.

The fact that they've only found one document and only on the personal laptop of a single employee seems to suggest that they actually did a good job in due diligence.

Does anyone know how many former Waymo engineers now work at Uber?

Why's this guy being downvoted? In an era of "but her emails" are we really surprised that an employee's phone could have hundreds of for example corporate emails leftover, if not other documents depending on what tech they use.