Likely from airplane. Secondly, camera sensors are sensitive to a broader frequency range than the human eye. It's why filters are usually placed on sensors to restrict frequencies. The question becomes, were they taking pictures and the fire and discovered the beams? Did they see the disturbance such a beam would make? In do agree, is very unlikely the beam itself would be visible. It is however possible atmospheric distortion makes them visible. Lots of stuff in the air, including moisture.