Because I can think logically how the object pictured could be a binary system that has blue star and a red star, and as they rotate, you get the full spectrum of visible colors, thus giving it its quite odd appearance. Also, Sirius A is 1.7 the diameter, and 25 times the brightness of Sol, and is only 8.5 light years away.
P.S. I wish I could have a UFO sighting like you mentioned, Peregrinus
P.S. I wish I could have a UFO sighting like you mentioned, Peregrinus