The Wheel Sensor stores speed, distance and time for all rides, whether it's connected to a phone at the time or not. If there are rides that appear to have happened before you bought a new bike, they are most likely test/demo rides that were done at the Cannondale dealer. Or, for a secondhand bike, they are rides that were done by a previous owner.
In your ride history those rides will not have any location data at all, and will appear with the note, "Only Wheel Sensor data available."
You may choose to delete those rides from your ride history by tapping into each individually and selecting "Delete".
Note that if you delete rides from your history, the total distance for the bike in Activity and Garage will change. However, the Wheel Sensor odometer value, which appears in Bike Details > Sensor, will not change - much like the odometer on a vehicle.
Further helpful info on how the sensor and phone app work together is here.