Musar sobre Números 16:4

I have mentioned already that at the beginning of his career Moses was on the level of איש. When a person is referred to as איש, this means that he is someone of substance. Later on Moses rose to higher levels and became אלוקים. In his Moreh Nevuchim, Maimonides explains this as follows: All the prophets receive their prophetic inspiration by means of a go-between, i.e. angels who are called אישים, because they are the medium through whom men are granted prophetic insights. This rule did not apply to Moses, however. Moses enjoyed direct inspiration. Maimonides goes on to explain the words of our sages on Numbers 16,4 where the Torah describes Moses as falling on his face after hearing the accusations of Korach. According to Sanhedrin 110, Korach accused Moses of adultery. This seems a very strange accusation, seeing that Moses had been faulted by his own sister for separating from his wife, abandoning marital life, due to his calling as a prophet who had to be "on call" at all times in case G–d wanted to communicate with him (Numbers 12). Why would Korach level such an unreasonable accusation against Moses?