Apple Pencils working on 2 iPads

We randomly experienced this during exam preparation.
Both Apple Pencils 1.Gen could be used interchangeably on both iPads.
Any guesses or resources on what went wrong during?
Somehow the same encryption keys must have been used for communication.
Apple states that the pencils can only be paired to ONE device.

We are CS student and really interested on finding out what happened here!

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