why call it error ? there was no undefined behavior; someone actually implemented and tested whether it worked properly. why not call it a mistake? this was a mistake. calling it an error makes it sound like it was not on purpose.
If you step into the street in front of a truck while reading Hacker News on your phone, it's a mistake. You wouldn't have done it had you been paying attention.
If you step into the street in front of a truck because you think the truck is farther away than it turns out to be, it's an error. If you are playing baseball, and you estimate the vector to intercept a ball rolling along, and you touch your glove to the ball but fail to actually catch it, it will be classified as an error, You made an estimate of what the circumstances were, and it was wrong and you acted on purpose.
I'm not saying dictionary.com is the be-all and end-all of dictionaries, but their definition of error uses the word mistake several times. https://www.dictionary.com/browse/error
I get it though, there is a subtle difference. I'm just saying both terms mischaracterize (intentionally) what I think was likely a very intentional, knowing and calculated action by Twitter. I'm asserting without proof that there was no inattention as in your first example, and no miscalculation as in your second example.
The baseball example is problematic because "error" has a game-specific meaning just like "run" and "base," and whether you commit a mistake or an error, they will both be recorded as errors.
I was wondering about this as well, ie. if there is a qualitative difference between error and mistake. (English is not my first language, so can't really tell.)
IMO "mistake" implies an incorrect choice, whereas "error" implies an incorrect result. A mistake may or may not cause an error (and an error may or may not be caused by a mistake). There seems to be an element of "could have been done differently" in "mistake" that is absent in "error".
Recently I read an article saying that programmers should reserve "error" for the mathematical usage of "distance from correct result" (as in, behavior of the program), and refer to their bugs and other mistakes as "blunders" instead. I have to think on it more but I like the overall direction of the distinction.