it was never trained to do insider trading, or any kind of trading. it was trained to predict the most likely next word given a bunch of previous words as input, then trained to not do that when the next word would be racist/destructive/etc. it turns out that's super versatile, and can be used to approximate a lot of other functions, like trading on the stock market.
as for sources of information, kinda the big problem with it is how unselective openai were when picking training data. they just loaded all of reddit and wikipedia into it, then dumped a ton of other random shit in there as well.
what i'm getting at is chatgpt is really powerful (duh) but it wasn't created with nearly the intentionality most people think it was, and it doesn't have a lot of the power that people think it does.