Given that Russia is descended from a state founded in the Middle Ages by the Rurikids, what did he consider to be its antique precursor?
No idea what he was getting at. The area that is now Western Russia was inhabited by Slavic, Finnic, and Baltic peoples and the societies was tribal and very much clan based. Around the same time as Alexander, the Slavs were migrating west into what is now Poland. However, there was no polity you could point to and say it was a precursor of the modern Russian state.