Importantly, this explains why a number of Facebook on iOS users were reporting that the app was showing background usage even when background refresh was turned off. Many people thought Facebook was using a private API to track people when they weren't using the app. In reality, it was just a mistake. This is a great example of Hanlon's Razor [1]

[1] "Never attribute to malice that which is adequately explained by stupidity." https://en.wikipedia.org/wiki/Hanlon%27s_razor