Let us examine that claim. In 2015 a total of 449,826 thousand megawatthours of electricity was generated within the state of Texas. Of that amount, 44,833 thousand megawatthours were generated by wind turbines. Thus we see that 10% of the electricity generated in Texas and dumped onto the Texas grid was generated by the wind. Thus anyone extracting electricity from the grid received just 10% of the electricity generated by the wind.EIA Electric Power Annual Report
Since the 2016 data will not be available for some time, assume the ratio of wind generated electricity to total generated electricity remains approximatly the same at 10%. Thus in 2016 the electricity that Georgetown extracted from the Texas grid contained no more that 10% generated by wind turbines.
Thus we can see that Georgetown purchases wind generated electricity in excess of current demand, but once it is loaded onto the Texas grid out in Amarillo, eveyone extracting electricity from the grid gets 10% generated by the wind. The only way Georgetown can claim their electricity is 100% green generated is to contruct their own transmission lines between the city and the generators.