There could be any number of explanations that would account for the slave not having eaten or drunk for three days and three nights; I mentioned only one, but it may or may not be the correct one. The point is, the Bible says the slave hadn’t eaten or drunk for three days and three nights, so we know it is true. The exact reason isn’t at issue; we simply don’t need to know every detail of the reason or reasons. The fact that the Bible says it is true is sufficient.