Yes, but most Russians living in Estonia are post-1945 colonists or descendants of post-1945 colonists. I had imagined that the bulk of the population have a long and storied history in Estonia, but they don't. For example, no ethnic Estonians were allowed to return to Narva after the war, and was instead settled overwhelming mostly by Russian colonists. Narva is the third biggest city in Estonia, and 88% Russian. Pre-colonisation it was majority Estonian.
So the border is old but the ethnic borders are very new and based on very recent Russian colonisation.