I think it is mis-stated, but I appreciate the intent. I believe the statement may refer to AEI specifying configurations that may be or may not have been standard configurations in the USA. It is not a question of quality, but specifications.
Stag Arms produces excellent rifles at reasonable costs because:
A: They are one of the largest manufacturers of M16 FOW (family of weapons) parts in the USA.
B: With almost 40 years of continuous M16 FOW manufacturing experience, experience speaks. They are a US Dept of Defence certified M16/M4 Subcontractor and learned how to make parts over 30 years cutting M16 parts almost exclusively for the local CT M16/M4 "Primary Contractor".
Only Colt has been manufacturing M16 FOW parts for longer than Continental Machine Tool of New Britain CT, Stag Arms 'Parent' (literally) company.
Hope that answers your question. If not or if you or anyone else have any questions, don't hesitate to ask.