I believe he's referring to the fact that he was at one time the maintainer of giflib (or libgif) and that he contributed some code to libpng. Since these are, he claims, vital to all those items you mention then we are all using his code.
That's right. People asked about this in the comments on the post. His answers are here:
http://esr.ibiblio.org/?p=1404#comment-242133
http://esr.ibiblio.org/?p=1404#comment-242156
Bottom line: libgif and libpng.
CompuServe described GIF, and then Gershon Elber and I made an open-source implementation that became ubiquitous
Worth noting that multiple years span the time between when Elber actually wrote giflib and when ESR added 2 functions and 3 utilities to it.
Any guesses? I'm pretty sure this phone doesn't use fetchmail.