Lol. No, the people were not eating magic mushrooms for breakfast. The story is a metaphor about what part the priests play in leading the people and how they did it. It's just told in a way that everyone can get something from no matter what their beliefs might be.Also, it was not just the priests who ate manna, but it was all the people. So to imagine that the people were walking around for 40 years, in the desert, high on magic mushrooms, seems not to make sense.
Some things were never revealed literally.