After doing some more research I found out that the email was sent in error due to a techical problem with Frontier' reservation system.
Frontier Airlines has released the following statement:
"Earlier this evening, a technical problem in our reservation system caused an email to be sent to a number of our customers indicating that their upcoming flight on Frontier Airlines had been canceled. This email was sent in error. We apologize for any distress this may have caused our customers. You may confirm the details of your trip by entering your confirmation code on the My Trip tab on our website, or the My Flights section of our mobile app. Once again, we sincerely apologize for this inconvenience."