You appear to have it correctly, Vika. Here's a translation from the Russian Primary Chronicle for 863-866:

"863-866 (6371-6374) Oskold and Dir attacked the Greeks during the fourteenth year of the reign of the Emperor Michael. When the emperor had set forth against the Saracens and had arrived at the Black River, the eparch sent him word that the Russians were approaching Constantinople, and the emperor turned back. Upon arriving inside the strait, the Russians made a great massacre of the Christians, and attacked Constantinople in two hundred boats. The emperor succeeded with difficulty in entering the city. The people prayed all night with the Patriarch Photius at the Church of the Holy Virgin in Blachemae. They also sang hymns and carried the sacred vestment of the Virgin to dip it in the sea. The weather was still, and the sea was calm, but a storm of wind came up, and when great waves straightway rose, confusing the boats of the godless Russians, it threw them upon the shore and broke them up, so that few escaped such destruction. The survivors then returned to heir native land."

Oskold was a contemporary of Rurik of Novogorod and must have had Rurik's sanction to attack Constantinople.