Not sure if the circumstances are compatible or not but I have seen some cases at US Embassy Manila where people got a message like that before they even had an interview date. Mostly when they had expedited thier cases. Consensus in those cases seemed to be that it was probably just some kind of auto generated system message and just meant the Embassy was actively working on the case. At least in the Manilla cases people did seem to go on to get real interview dates not to long after they received false cancelation notices.
