The article was explicit about this. The A->C message was initiated from thread A before the A->B message. So causally the B->C message is after the A->C messag

The article was explicit about this. The A->C message was initiated from thread A before the A->B message. So causally the B->C message is after the A->C message, because it's after the A->B message (which itself is after the A->C message). But in this case causality was broken. It wouldn't be confusing if the A->B message was sent first, because then the B->C message would be unordered relative to the A->C message. Depending on the processing at B it would be totally normal that one or the other would reach C first.