But since they did not appear to be malicious and because I had no grounds for condemning them, I never mentioned the incident to anyone. I understood that they were doing so out of love, not as worship. Certainly no pious Shia ever prostrated for anyone but Allah. To bow down before a respected person without considering him Allah or to fall down on the ground and rub one's face on it, is not polytheism. It is the result of intense love.
Prostration depends on intention, and intention is a matter of the heart.
Only Allah knows our heart's intentions. For example, we may see people lying down on the ground in the manner of ritual prostration. It is true that prostration to anyone but Allah is not proper, even though it be without any intention. However, since we are not aware of their heart's intention, we cannot call it ritual prostration. For example, the Prophet Joseph's brothers prostrated before him.