Schedule reminder created for 'x' hours after event end date fetches all past event participants.

https://civicrm.stackexchange.com/questions/17974/if-i-create-a-scheduled-reminder-for-event-feedback-eg-16-hours-after-should-i

As mentioned on SE, I set up a scheduled reminder to be sent out 2 days after the end date of an event.
When the reminder was saved it sent an email to all contacts that had ever historically(even 5 to 6 years before) attended an event, about 3,500 emails.