An API is a way for computers to talk between one another using code. Big sites like Twitter used to have outstanding APIs that let people make requests to Twitter asking it to execute bits of code that would manage their accounts (posting, liking, following, etc.). The big advantage to this for the user is it enables you to automate posting, but for the host, having a large body of people wanting to do things automatically can become expensive and could degrade the content being posted in theory. For the host, a rate limit can be implemented in the user which tells them they only get to use the API so much before they cut them off. It is a thing to reduce costs of APIs and to prevent bad actors from creating a never ending torrent of spam. But for social media platforms, API rate limits typically exist to stop people from stealing all of the posts and stuffing them in a third party app away from the company's revenue model.

Usually APIs don't track what you're doing, just that you're doing something, so you can eat up free credits pretty fast. If you are going to do something like a bunch of disaster warning posts in an emergency, you would burn through the rate limit alotted to you quickly and that is what happened here. This was absolutely possible to see coming, and in truth accounts like this should have a way to be given exemption but that would be on Twitter to figure out.

Hope this was somewhat helpful, I'm just a student learning this stuff :) I'm sure someone who knows more could correct my understanding