What It Is Exterior Angle Inequality Theorem?

The exterior angle inequality theorem is a triangle theorem.  

Since
we know that the exterior angle = the sum of the 2 remote interior
angles by a previous theorem (the exterior angle theorem)... We know
then that the exterior angle must be larger than either of the angles
that need to be added.

It's like saying that since 60  + 40 = 100, then 100 must be larger than either 60 or 40 -or-
100 > 60
100 > 40