Mei Marom 30:1

The Mekallel's cursing of Hashem was because of the Lechem Hapanim. Rav Charlop explains that the Mekallel had established in his mind a reality that bread gets colder and staler as it sits, and he refused to move from this perception. In his mind, it was impossible for a nes to take place and allow it to remain fresh for days. In doing so he cursed Hashem- literally he was yikov Hashem- he "threw Hashem out of the world" by saying that Hashem is limited to his version of reality. Therefore we undertand that he was a ben ish mitzri- mitzri implies boundaries- he was confined by his version of reality, and refused to see any other way of the world functioning.