You weren't picked for soak test yet. You've been invited to join the pool of possible soak testers. This time around, the soak test pool is limited to 1000 users and not everyone that is invited and fills out the survey will be on the soak test. Shortly before the actual soak test starts, and confirmation email will be sent out to the soak testers with a link to a private community for the soak test discussion. Within a couple days of that email, you'll get the OTA notificiation on your phone.