Particularly in very competitive professions like commercial music where lead singers are often required to compete with one another for attention, chance meetings can lead to collaborations that can change the face of the business. When people like Jagger and Richards meet unexpectedly without time to form any preconceptions, they can end up just talking and learning what aspects of the business and aesthetics they have in common.
Whether people meet by coincidence or if they agree to meet someone beforehand, it is important to record these events. Meetings are important and set the place for important discussions to take place, we can not dismiss them just because they were not premeditated like others tend to be most of the time.
Yes, random meetings such as Mick Jagger and Keith Richards meeting at a train station are very important because they affect the evolution of humanity. These musicians have contributed to the cultural patchwork of our world. They have made history with their music. Meetings between individuals like them are monumental.
Of course the chance meeting between Mick Jagger and Keith Richards is important, and similar random meetings are also important. If the meeting had not occurred, the events that followed would not have occurred either. For example, if your mother had happened to not meet your father, you would not be alive. A random occurrence turned out to be important.