The story refers to https://en.wikipedia.org/wiki/Mithraism https://en.wikipedia.org/wiki/Mithraism, not Zoroastrian proper. The old synthetic polytheisms were

The story refers to https://en.wikipedia.org/wiki/Mithraism https://en.wikipedia.org/wiki/Mithraism, not Zoroastrian proper. The old synthetic polytheisms were all pomp and circumstance, with the elite atheists, and poor treating it more like fortune telling + some light collective obligations for sacrifices and whatnot + entertainment. They weren't a serious competitor on religious grounds as there was no fervor of belief. Mithraism, on the other hand, was another "new-age cult". Like today's, the older religious origins (Zoroastrianism) probably did more to legitimize it / add mystique than actually reflects a strong continuity of belief. Mithraism had the zeal and singular focus to be an actual competitor to Christrianity.