How is this guy doing this exactly ?

So I noticed this url indexed on Google a couple days ago, but I don't understand exactly what this URL represents and why it's indexed in Google.…M6Ly92ay5jb20vcGFnZS0xNTYzNzk1MzNfNTI4NzI0MDI

can anyone help me understand what's going on with this url, especially the long string of characters at the end ?