Example: logs of search queries that suddenly trend with adverse information about companies. Those logs are not public, in fact you need to buy them, but they have real signal (thus material and nonpublic), and are perfectly legal to buy and use. Satellite photos to estimate material stacking up outside a factory, or how many cars are in the parking lots of retail stores. Mobile data that has been statistically tied to foot traffic in stores. Credit card purchase data (not public! very material! perfectly ok!) I could go on forever
Go ask a lawyer this is a big space
EDIT: Yes exactly, ITS HAS TO BE CONFIDENTIAL TO THE COMPANY AND THUS TAKEN FROM THE COMPANY LIKE I SAID ABOVE. Your explanation implicated all the cases I described. You haven't seen how explicitly rich are the sources that I mentioned above, they are very very definitely information about the companies that are traded