The footnotes on page 11 give a good explanation.
For the most part, Austria, Hungary, and Poland are broken out separately according to their present borders, even for the periods when they weren't separate countries.
How was the data gathered? Depending on what you asked a Hungarian from 1850, you might have gotten 3 different countries.
Where are you from? Austria.
What nationality are you? Hungarian.
What state are you from? Germany.
Where are you from?
1853: Lemberg in the Habsburg Kingdom of Galicia and Lodomeria, the first city in Europe with street lights! I'm Galician.
1923: Lwow in Poland, the city that bravely defended against the Red Army! I'm Polish.
1953: Lviv of USSR! I am a Soviet citizen.
1993: Lviv of Ukraine! I am Ukrainian.
And this doesn't include some shorter term changes such as Distrikt Galizien in 1943.