Ironically, al-Sistani is himself an Iranian.
True, he was born & raised mostly in Iran. Just as Ali Larijani, chairman of Iranian parliament, was born in Iraq. But Sistani has issues with Khomeini’s invention the doctrine of Velayate Faghih (Islamic Jurisprudence), which is the foundation of the current Iranian regime & doesn’t follow it. That’s why many Arab shiites see him as their spiritual leader.