It depends entirely on the air conditions. If the jets crossed paths, they would have crossed each other's downdraft wake, and that might have been enough to promote the condensation process. Or, if they were both in climbing flight, they might have simultaneously reached the altitude at which contrails form.
Have you ever seen a lenticular cloud capping a mountain? That happens when moist air is coming along the ground, rises over the mountain--and when that happens, cools down and condenses water droplets---and then flows down over the lee of the mountain, where the air warms again and the droplets evaporate and vanish. It seems like a stationary cloud, but it is really a transient effect in an airstream. Contrails are only clouds.
If you would rather believe your ignorance than someone who understands the phenomena, you are in a pickle.
It depends entirely on the air conditions. If the jets crossed paths, they would have crossed each other's downdraft wake, and that might have been enough to promote the condensation process. Or, if they were both in climbing flight, they might have simultaneously reached the altitude at which contrails form.
Have you ever seen a lenticular cloud capping a mountain? That happens when moist air is coming along the ground, rises over the mountain--and when that happens, cools down and condenses water droplets---and then flows down over the lee of the mountain, where the air warms again and the droplets evaporate and vanish. It seems like a stationary cloud, but it is really a transient effect in an airstream. Contrails are only clouds.
If you would rather believe your ignorance than someone who understands the phenomena, you are in a pickle.