It is because a RDS radio station that transmits time signals is tuned to; and the time in this time signal is different from the clock time set in your system. The clock time in the system would be changed automatically according to the time signal of this RDS radio station. This is not a failure.
Note: The accuracy of the time in the time signal depends on the RDS station.
What is RDS?
Radio Data System (RDS) is a service that allows FM stations to show information such as the station name.