The official census data released by the Government of India disproves the claim.
As per the 2011 census data, the corresponding was 54.73% (1,82,82,492 / 3,34,06,061 x 100). Based on the comparison the Hindu population has decreased in Kerala.
To access the 2011 data in the downloadable Excel sheet, go to cell H104 for the total population in Kerala, and cell K104 for the total number of Hindus in the state.
The 2011 census data is the latest Indian demographic statistics available as of February 2020 and the next census is due in 2021.