In one of Grigori Perelman's papers, on the first page there's a footnote where he says,
∗St.Petersburg branch of Steklov Mathematical Institute, Fontanka 27, St.Petersburg 191011, Russia. Email: firstname.lastname@example.org or email@example.com ; I was partially supported by personal savings accumulated during my visits to the Courant Institute in the Fall of 1992, to the SUNY at Stony Brook in the Spring of 1993, and to the UC at Berkeley as a Miller Fellow in 1993-95. I’d like to thank everyone who worked to make those opportunities available to me.
Is this footnote from his famous paper meant to be a joke, or is it actually necessary to list one's source of funding, even if it is just one's personal savings?