Alternative hypothesis: the reported number of drones isn't real (anything the Trump government says about "cartels" can be assumed to be made up). The military got increasingly on alert, with senior officers pushing to get a shootdown on one of the not real drones. Therefore the laser operators end up firing on the first drone they confirm seeing.

Compare the MH-17 incident. See also https://en.wikipedia.org/wiki/Gatwick_Airport_drone_incident , which also involved no confirmed actual drone.