The story you're refernecing about Zoroastrianism was added centuries later and was not part of Zarathushtra's teachings. The Gathas are universally acknowledged to be his actual words (one of very few writings by the actual founder of an ancient religion). So we can seperate the actual person from the legends that followed later. In the Gatha, Zarathushtra never claims nor implies God spoke to him. To the contrary, his poem was a prayer of sorts to the Gods.
"Zarathushtra's theology is always projected with a moral dimension, Asha always carries the joint meaning of Truth and Righteousness. Thus we comprehend the world as an intrinsically good, divine creation, contaminated by evil, but capable of being perfected by the actions of humans by reason of their capacity of moral choice. Human action can promote good and reject evil leading to its ultimate banishment from the world, though it may continue to exist as a conceptual possibility."
"The focus of Gathic teaching is one of a world afflicted with suffering, inequity, and imperfection, the goal being to transform it and bring it to perfection, that is, in consonance with Truth, by the comprehending power of the Good-Mind. Such a perfecting world would progressively bring satisfaction to all the good creation. And it would inaugurate the desired kingdom, Khshathra Vairya, where the ideal society would manifest peaceful social existence in which all interests would be harmonized and balanced in a just order, for that is an implication of Asha. This achievement depends on enlightened human thinking and right-minded human resolve."
- Dr. Kaikhosrov Irani
Hope that clears things up a bit :)