P.S. You will probably say "yeah, but people held USSR passports, did they not?, does it not mean they were citizens of the USSR?"
My answer is this: No, it does not. every USSR passport had the field that said NATIONALITY (I looked at my parents' USSR passports when I had this dillema), and there, in that field to be more precise, it said: ukrainian, russian, latvian etc.
Just like every EU passport now has a red color cover and words "European Union" in their respective language on every passport... It does grant freedom of movement, and technically you are a EU citizen, but I am sure people put Germany, France, Spain etc. as their citizenship...
I hope you see what I am saying...