There are those without any inside information that can make a good educated guess as to what is going to happen. Due to their certainty they then start a rumour as there is a good chance they will be correct. This is done to increase their own standing as someone in the know.
A clue to what they know can be deduced, as to whether they are indeed insiders, by looking at their track record. For instance did they predict EasyJet’s new winter only domestic program to Southampton weeks in advance of its announcement?