The german to SA passport is sort of legal. Normally you have to give up your german passport when taking up another citizen ship. However in the late 1980's the South African gov was seeing a large number of young men getting foreign passports by vertue of proxy. The British was really big at that if you had a grandparent from the UK you qualified. This mean't the boys could dodge the draft. As a result SA passed law requiring all children to take up SA citizenship at the of 12 even if they wer not born in the country. I was caught up in this mess too.

Since my german passport was my birthright (I was born in germany) ,and the german gov was not a part of this regulation, the german gov decided that I could not loose my birthright because another country was forcing its citizenship upon me. So one the morning of my 12th bithday I went to the german consulate handed over my german passport and was given a note saying as of now I was not in poscession of a german passport. I then went around the corner to the post office (they handled gov. business back then) handed over the note and picked up my new documents. They you went back to the german consulted to pick up your old passport and off you went. The kids with these docs did the following - within the country you used your SA docs leaving the country and outside you would always use your german / international docs.

While it was still unclear weather or not I would loose my birthright there were plans in the pipline for me to move to grandparents and finish school there if the german gov had decided that I would automatically loose my birthright. 10 year down the line I was glad to still have my german passport.

However the US bit is as far as I know only correct if the person was born in the US since a US citizen never looses his/her birthright even if they take up another citzenship - it is however from the german side you are required to give it up if you want to take up german citizenship. So your friend is possibly also one of these special cases.

Honestly? It's none of CBP's ....ing business what your ties to Austria are. If the US has a problem with you having dual South African and Austrian citizenship, then they need to take it up with the appropriate authorities in Austria and South Africa, not take it out on you by harassing you at the border.

South Korea forces kids that have dual citizenship to give up their other citizenship at age 18 to retain South Korean citizenship, probably for the same reason South Africa did the same. But it works against them because 99.9% of them gave up their South Korean citizenship and then proceed to leave the country (and some parents fly out to places like the US and Canada that grant jus solis citizenship to have kids)

Given its relatively safe borders, why did South Africa even have a draft in the first place?

Back then it wasn't so quite. Angola, Mosambique just to name 2 hot spots of the time. SA was in the thick of things back then and thats why the draft was so important. Afterwards in the 90`s it was to try and curb the brain drain that was causing problems for the economy (although the propaganda would never fess up to that)

You have to remember back then conscription was limited to a small fraction of the population (i.e., white males) and the apartheid government had to sustain minority rule in the country.