Besides the fact that, like Bluehawk said, this is too big and too long-running and too involved for it to be an inside joke-- there's tulpas/ tulpa-like beings in history, like Socrates' daemon, Carl Jung's tulpa, authors with characters that take on life of their own, there's some articles on it, and research being done...
Or you could come into the IRC and talk to a few hosts and their tulpas, see for yourself.
Some links to stuff mentioned above, h/t /u/Nobillis :
Veissière, Samuel, PhD, Talking to Tulpas: Sentient Imaginary Friends, the Social Mind, and Implications for Culture, Cognition, and Mental Health Research (McGill University, 5 Sept., 2014), “ongoing study”.
Taylor, Marjorie; Mannering, Anne M., "Of Hobbles and Harvey : The Imaginary Companions Created by Children and Adults" in A. Goncu & S. Gaskins (Eds.) Play and Development: Evolutionary, Sociocultural and Functional Perspectives, Pg 227-249 (Lawrence Erlbaum, 2007).
Taylor, Marjorie; Hodges, Sara D.; ADÈLE KOHÁNYI; "The Illusion of Independent Agency : Do Adult Fiction Writers Experience Their Characters as Having Minds of Their Own" in Imagination, Cognition and Personality, Vol. 22(4), 2002/2003, pg. 361-380 (Baywood Publishing Co., Inc.: U.S.A., 2003).
Dionne, Karen, "When Characters Talk, Writers Listen" in The Huffington Post (U.S.A., 19 March 2014).
LUHRMANN, T. M., "Conjuring Up Our Own Gods" in The New York Times (U.S.A., 14 October, 2013)
Simler, Kevin, "Neurons Gone Wild" in Melting Asphalt (U.S.A., 10 December, 2013). Also published as:
Simler, Kevin, "One Brain, Many Selves: Demons, Tulpas, and Neurons Gone Wild" in Psychedelic Frontier (U.S.A., Jun' 24, 2014)
Okibi, "Socrates and the Daimon : Let the Father of Western Philosophy rock your socks" in The Daemon Page (daemonpage.com).
A number of historical references to tulpa-related things have been collated by a member of Tulpa.info .
And, for an off-the-cuff (but not necessarily completely fleshed-out) theory on tulpas there is Pleebs Tulpa Lecture from about a year ago. Pleeb is the owner of Tulpa.info .