I dont think religion plays a big role when deciding things like that in Iran, many reformists in Iran are weirdly pro-western and since 2015 deal went kaput they have been trying to get back on that horse.Perhaps it's a religious thing? If you're a fanatical Shia zealot - as the Iranian regime are - you'd prioritize relations with:
1. Heretics (Sunni);
2. Infidels (Christians); then
3. Heathens (Buddhists, Hindus, etc.)
in that order.
Edit: People of the Book entitled to dhimmi status, those who shirk are lowest of the low (apart from apostates):