Is this footnote from one of Perelman's papers meant to be a joke, or is it mandatory to list one's source of funding? 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: perelman@pdmi.ras.ru or
  perelman@math.sunysb.edu ; 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?
Indeed, funding agencies require authors to acknowledge their funding, but it's not mandatory to acknowledge personal resources. 

To me, however, that footnote doesn't sound like a joke at all, but a sincere acknowledgement of those who have supported him during previous years allowing him to have savings (and during those visits he might have worked on different topics). 

That said, there are certainly a lot of joking acknowledgments around.