What they are a guru in varies by market but you have training guru's, diet guru's, life guru's (by far the most nauseating), business guru's, supplement guru's etc. In today's "take credit for anything" business model these guys (and gals) are in overabundance. Besides being irritating, what's the problem right? Keep reading.....
Want another example? How about the ever popular term "muscle confusion." P90x made this a household term but in all actuality this training technique can be traced back to ancient Greece. Yup, you read that right. The ego of the average trainer is so small that they can't help but to engage in this behavior. I worked alongside a guy who would randomly take credit for inventing exercises, - i.e. "I invented the lunge," as well as venturing into life guru territory by inventing a test for clients to take that was nothing more than Dr. John Travis' wellness continuum (created in 1972 by the way) in a very, very watered down form..
The nutrition and supplement industry are no different. I have read articles dating back to the early 1900's on the promise of low carb nutritional protocols. You could make a drinking game out of how many people have tried to package themselves as the driving force behind that idea. That's not even counting the enormous amount of offshoot dieting programs that have been developed as well such as IIFYM, Intermittent Fasting, so on and so forth.
As the saying goes, "one good turn deserves another." Which leads us to the last and most treacherous guru out there - the life guru. The life guru is kind of a catch all category, as they come in lots of shapes and sizes, and they cross multiple frames of reference - training, nutrition, coaching etc. Light on science and heavy on metaphysics/new age spirituality or "woo," the life guru has all of the answers for your life, despite not having all for their own. Part "feel good" and part spiritual babble, the life guru is probably the one who can do the most damage to your life... at least to your wallet (another sign of this garbage is the exorbitant fees most of these people charge) just ask The Beatles.
In summary, maybe my years in this industry have left me jaded and this is just me spewing venom for venom sake, but at least its my venom. How do I know? I created it!