Checking for wheat would not be that hard, as wheat kernels are roughly 15-30 times larger that a quinoa grain.
If you broadly define “midi demidgin” as “growing in “sharvitim” the it would qualify as kitniyos, HOWEVER,
if you say that gezeras kitnoyos did not “cross the Atlantic” and that anything native to the Americas (the potato for instance, and also zachur latov, peanut oil) is not kitniyos, then quinoa is also not subject to the gezera.