Yes, most likely, your cluster wouldn't work if the connector came undone.
Couple things to check then: visually inspect the connector, ensure that a 'pin' didn't come out affecting the speedo.
The other place to check (and you should pull the left side to inspect) is to check the speedo pickup sensor. The pickup sensor is located on the sprocket/clutch slave cylinder cover on the left side. If you look at your shift lever, where it enters the motor, the sensor is a few inches above that - held onto the cover by one screw.
Make sure that the sensor is mounted correctly and if it is, follow the wire up the left side of the frame (this is where pulling the plastic helps) - make sure that the connector is secure.