Not necessarily the true. Back in 2012, a guy from Yemen received a wild card in taekwondo and he eliminated silver medalist from Beijing in the first round. And it's not like he was some good and known athlete who just missed a qualification, similar to the athletes that got wild cards this time. Plus, like intoronto said, taekwondo is very popular in a lot of small nations.
From my experience of watching, it's more common and easier for weaker athletes to get a RSC in boxing or FALL in wrestling rather than RSC in taekwondo.