Rule of Thumb: minimize direct and indirect impact on the root system of established trees. However, we live in a world where we want services, and sometimes these services require minor sacrifices to aesthetics, vegetation, or structures. I truly believe most utility/cable companies and their employees are conscientious stewards who do not wish to inflict undue harm to native vegetation. However, there are times when some disturbance is necessary to facilitate service maintenance, upgrades, etc. Who knows, maybe the employee should have run an aerial line rather than trenching the cable through the middle of your yard—was this an option? I don’t know and to be honest, I really don’t want to discuss that issue via this forum.
Instead, let's focus our attention on this oak tree. Please monitor the tree for signs/symptoms of reduced vigor: crown dieback, abnormal foliage, wilting, etc. Make sure you are following a proactive watering and fertilization regiment. Make sure to water your lawn/trees during periods of drought. Please contact your local UI Extension office or a local certified arborist if you observe any significant symptoms indicating reduced vigor.
Best of luck!