Please tell me the name of the person, and I might be able to help you more. Also, the answer might be, back before WWI and WWII, Russia owned provinces of Lithuania, Poland, Ukraine, etc. As they had not gained their separate independence yet. For example, a couple of my ancestors stated their birth place was Minsk, which is today Belarus; However, it was part of Russia back then. So if your ancestor said they were born in Poland back then, it could have been so, or it may have been a Polish province that Russia controlled.