Google was originally scheduled to make some announcements on June 3 that were on hold due to the cancelling of Google I/O. It was also supposed to release the Android 11 Beta on June 1 for the public (Android 11 is still under an extended "Developer Preview" phase). The event was recently postponed due to the ongoing tension across the United States. Despite Google's decision to postpone the event and release of the Android 11 Beta, it seems that the update was inadvertently pushed to some small number of Pixel devices. This, as reported by @mishaalRahman on Twitter. It's unclear whether...
Source: https://www.gsmarena.com/google_accidentally_pushes_android_11_beta_to_some_pixels_despite_its_delay_announcement-news-43521.php