Depends how technical you want to get... I guess in terms of pure language meaning, no - as a lie is a spoken untruth... If the initial promise/statement was made with no intention of following through, then it is a lie, but if it was made with the best of intentions but things happened to change the circumstances, and there was no explanation given, then it isn't a lie exactly, it's a broken promise/commitment... does that help?
On the other hand, if they turn around and SAY they never promised/committed in the first place, then that IS clearly a lie.