Maybe although I don't know how they would identify the "safe" drivers among the folks that are just mindful during the evaluation period. Perhaps they weed people out who seem to drive routes their system doesn't handle well. Still, it seems like the rollout plan would be a good way to collect a training set that is biased toward safer driving habits.
Also, this sort of short evaluation seems like it wouldn't mitigate that much PR risk. It may even increase bad press if things go poorly and people point to it as an indication that they knew it wasn't ready.
Smells more like they know this release is risky and want to minimize the PR risk.