I would think it's an edge case of correlation, but still correlation (100% of the time it has had this error, it was on a leap day, 0% of the time it was not)
It might appear as a correlation due to sampling error, but the two variables have no dependence with each other. There is no correlation with it being February 29 and the bug that was described.
I think that's exactly what OP is trying to say when they say 'correlation, not causation'. There is no causal link between 29th February and the bug, but they happened at the same time (were correlated, i.e. had the relationship that they happened at the same time).
This is a fairly typical informal usage of the word correlation in my experience, and while it might not be _technically correct_ (I don't know, I'm not an expert), it's an often enough used idiom.
"Correlation does not equal causation" is a very important and pertinent concept in statistics, and I think we should aim to actually understand the concept instead of just trying to warp the meaning of the words to fit the example
The bug simply was not "a good example of correlation does not equal causation" as any statistician would use the phrase. That's my only point. OP is free to type whatever words he wants into the comment box and press send
