His concern is not that OnStar will fail to remove your name from the GPS location stream. It is that even without a name attached, the subject's identity can be readily inferred from the data itself.

If one looks at a stream of location data over time, and sees the recurrence of a particular location in a residential area, particularly at night, then it can be pretty well surmised that this is your home. And from that, it's a trivial step to get your identity. And bingo, the anonymized data is now re-identified.