By "restricted" I think Braztech was referring to their own company policy and not legal constraints pursuant to any jurisdictional body of law.
Bottom line...........they just don't want to send you certain parts.
No doubt acting on their legal departments advice.
Alotta lawyers I met and have dealt with on a professional basis are the scrubbed & polished (absolutely no dirt under those fingernails

) & very snooty "superior" liberal anti-gun type (even though they sometimes work for gun companies) and will throw obstacles in the way of acquisition of guns or gun parts whenever and wherever they can.
We think we need guns but they being lawyers and therefore superior to the common "redneck rabble" need to protect society from us and our "bare wire" primitive instincts.
I have to deal with their gibberish just about any time I submit a set of plans for approval and they can sure expand a project time line.
I don't imagine things are much different for engineers working for gun manufacturing companies.