Southern Baptists, by themselves, are 5% of the nation. The article says they are 1% of the military. Even with all those other folks, you only have 3% of the military. They're pretty clearly underrepresented.
All those other folks are not necessarily 3% of the military.
For example 29% of non-denominational Protestants are Evangelical but that 3% doesn't count non-denominational Protestants, since their church wouldn't be a member of the NAE. It doesn't even mention Assemblies of God who are 33% Evangelical and not even counted!
Furthermore it wouldn't be necessarily unreasonable to assume that Evangelicals have higher fertility rates than non-Evangelicals which biases their % since less would be of adult age.
I'll try this again. All Southern Baptists are unequivally evangelicals under every metric. They are five percent of the poulation. Even if all 3% of the military, who are evangelical, were Southern Batist, they would still be notably under represented. But there are more evangelicals who are not baptists. So the total undisputed evangelical population is higher than 5 percent. So, why are the undisputed evangelicals underrepresented?