I got fired recently about a month into the job for "underperformance" and "asking too many questions", but now 2 weeks later am getting an offer from JPMC and I'm a bit anxious and wondering about similar experiences.

This sounds like the company was not a good fit and you will be much better off at a different company. That said, you should cool-off a bit and try your best to look at things from the previous company's point of view to see if there is anything you would do differently next time in a similar situation... trying to make the most of a bad situation.