1) There's a range of speeds that are possible depending on what you assume the turning angle of the jet was. That range doesn't go anywhere close to the speed of sound.
2) The burden of proof is on those who make an extraordinary claim. There is a perfectly mundane explanation of the cause of apparently fast-moving object which is supported by available evidence. Even if that depends on some assumptions, you would have to demonstrate those assumptions to be false before a less likely alternative, i.e., that it was an extraterrestrial spacecraft, should be adopted.
