It's quite possible that the airline might not have caught the visa mistake either and even the immigration officer in Austria could have missed it unless flagged by the system. After all both people actually had a valid visa and their sirnames were the same. Unless the airline staff is very diligent and reads the name on the visa and compares it, they are unlikely to spot it. Since they are in a hurry and checking a lot of people, they might just glance at the visa and valid dates and issue a boarding pass.
A long time ago, when I used to have an Indian passport, I was driving from France to Italy with a girlfriend. The immigration officer stopped us and asked for passports. She didn't need a visa but I did and had obtained it. Only there we realised that the embassy had put a wrong entry date which was about 15 days later. The immigration officer at the border pointed this out. We explained that we were already there and had driven feom Paris and had all our itinerary planned. He was nice and told us to carry on! Mostly because I had a European girlfriend and they were less strict after the EU started. The girlfriend part helped me get a lot of last minute immediate visas as they had special rules for spouses and partners of European citizens and they were nice enough to declare me her partner in order to help me out.