Why can we consider that the Old Russian state has two origins?

In Ancient Russia, Novgorod was an independent city. All important matters were decided at a national assembly – veche. In 862, the leaders of different tribes invited Prince Rurik and his squad in order to rule and judge “by the truth.” This is how the princely administration of all important affairs appeared in Russia. In 882, the Novgorod prince Oleg (Rurik’s successor) captured Kiev and united the southern and northern centers of Russia. The city of Kiev became, according to Oleg himself, “the mother of Russian cities.”
The very expression “mother of Russian cities” corresponds to the Greek word “metropolis” (from the Greek words “meter” – mother and polis – city). Thus, Oleg called for the unity of all the tribes of Rus under the rule of the city of Kiev.