How do i remove the jailbreak on my stolen iPhone 5c?
Cydia is installed when the iPhone is jailbroken. iOS 8 Pangu Jailbreak installs the Pangu app during the jailbreak process. So the answer to your question is Yes, the iPhone is jailbroken.

How to remove the jailbreak from your iPhone


Connect your phone to iTunes
Do a factory reset
Restore back to the most recent iPhone backup


Following the above steps can restore the iPhone to factory condition and restore back to the recent backup through iTunes.