None of the sources I've read through itemize exactly what that means; they do mention that Uber was able to determine if a Lyft driver also drove for Uber, which means they knew the driver's personal details. Otherwise, if a Lyft driver did not also drive for Uber, I would assume they would not have personal information on the driver.

We'll find out regardless through discovery.

If you have overlapping GPS info of Lyft and Uber you know it's the same driver. If not, you could still order a Lyft to get their phone number and make them an offer.