Supposedly the Bering Strait between Russia and Alaska is only 51 miles wide at it's narrowest point, so wouldn't it have been comparatively easier for the people of Russia to have crossed that gap at that time, rather than the transatlantic voyages?
Hi, the tl;dr is that way back in the 15th century, Russian territory didn't extend to anywhere near NE Siberia, but the indigenous peoples who did live there did (do?) cross the strait, and in fact, had been doing so for a very very long time.
/u/kieslowskifan on Russians in How did Russia not know about North America before Columbus when you can see Alaska from the Eastern-most part of Russia?
/u/poob1x gives a broad overview in Is there any evidence of pre-colombian crossings of the Bering Strait?