All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
It is unbecoming of the Muslim to mock people. A wise believer refrains from such an act. Time is a great blessing; the Muslim's time is too precious to be wasted in such an action that brings no benefit for him or for Islam; rather, it may incur harm on him. Ibn ‘Abbaas, may Allah be pleased with him, reported that the Prophet, sallallahu ‘alayhi wa sallam, said, "Two blessings which many people squander: Good health and free time." [Al-Bukhari]
Instead of mocking people, the Muslim should be concerned with their situation and try to guide them to the truth so that he would earn the great rewards for that. Sahl ibn Sa‘d, may Allah be pleased with him, reported that the Prophet, sallallahu ‘alayhi wa sallam, said to ‘Ali, may Allah be pleased with him, on the Day of Khaybar, "Then invite them to Islam and inform them of what is obligatory on them from the Rights of Allah, for, by Allah, if Allah guides even one person through you, that is better for you than possessing the most precious red camels." [Al-Bukhari and Muslim]
Your assumption that the Hindu customs might have been revealed by Allah to a past generation through an earlier prophet is wrong and has no valid grounds. Hinduism is a pagan religion of disbelief that has nothing to do with the divine religions.
Allah knows best.