It's just standard wannabe edgelord bragging. Information about disposing human remains* is not hard to come by. It sounds like he was reading a lot of anarchist ebooks and similar online LARP material, and then repeating shit to try to sound tough and smart and intimidating.
(*not that this information is particularly good, because the people who do try to cleverly dispose of human remains with chemicals or the like seem to get caught 90% of the time. The real pros know to just throw them down a mineshaft)