The Muslim community in India is not really very centralized. Although there are few bodies who regulate and overlook everything, the community is largely divided by sects which goes beyond the regular Shia and Sunni (there are plenty more!). Now each of these sects has their own separate bodies, along with their own set of beliefs. So, if the leading body of a sect orders something, the followers (which basically includes imams of different mosques across the state and country) have to follow them, regardless they agree with it or not, fearing seclusion. This is an insider scenario that you won’t really hear much about. From the outside, it all looks normal. But from the inside, there’s a lot of politics.
Now coming to your question, yes, Kerala is celebrating Eid 2018 on Friday. And so are many people in parts of South India. The rest of the country – states in North – are scheduled to celebrate this festival on Saturday. The reason is same what I explained earlier. A leading body of a sect in South announced that they saw the crescent moon on Thursday evening. Their followers listened to them and are celebrating Eid 2018 on Friday, irrespective of whether or not they agree with them.
On the other hand, Shahi Imam of Jama Masjid Syed Ahmed Bukhari announced that moon sighting committee couldn’t find the crescent on Thursday evening, so the Eid celebration will happen on Saturday. So those who follow them will be celebrating Eid 2018 on Saturday. Plus, a lot also depends on when people of Saudi Arabia is concluding Ramadan. In India, due to the time difference, we usually celebrate Eid a day after them; they are celebrating on Friday, which makes Saturday ‘The Day’ for us.
Hope this answered your question.