Yeah, this can actually be said for a lot of different moves, not just the elbow.
I was in a competition once and I threw a round house kick, and the guy covered up but left his elbow sticking out. His elbow caught me right in the soft part on the top of my ankle, between my foot and leg. It caused an enormous amount of pain, and cause my foot to go completely limp.
Similar things have happened, as the article states, to my elbows, and also to my hands if something catches me on the wrist (But this is unlikely if wearing MMA gloves or wraps). Gotta learn all the in's and out's of any kind of martial arts move, or you're liable to do it wrong and eff yourself up.