Likely it is done using a PLL ( phase locked loop). You have two oscillators, one is the reference, the other one adjustable (voltage controlled). You divide outputs of both oscillators to arrive to a same common frequency, then feed these outputs to a phase frequency detector. if both frequencies are the same the ouyput of the detector is neutral. If they are not, the detector will produce a positive or negative voltage which is fed back to the adjustable oscillator and adjusts its frequency up or down to equalize the divided frequencies at the detector input. This way you can have two or more oscillators running at different frequencies derived from a common reference, as long as a common PFD frequency can be found for the dividers.
Have a read on PLL theory of operation to understand this better. PLLs are widely used in electronics so at some point you will run into it anyways.