Yes, I'm sure. Is is father or mother Austrian? There was a period in 2014 wherein children affected by this law were allowed to apply for Austrian citizenship - perhaps he took advantage of that. There has also been a recent change for descendants of holocaust survivors. I'm not sure about the german side of the equation.
i just learned that in 1983 when the law was changed, austrian mothers were offered to apply for austrian citizenship for their children born earlier. so if it wasn't made permanently retroactive, there was at least a time window to apply which is likely what my friend was able to take advantage of.
i don't know which parent is austrian.
my friend has both citizenships at least since their youth in the 80s. so whatever allowed that to happen must have been something in effect then. maybe a different temporary exception on either the german or austrian side.
See 'Obtaining Austrian Citizenship' here: https://www.bmeia.gv.at/en/austrian-embassy-london/service-f...