Slop.

I'm not even sure Stalin has anything to do with the specific borders being drawn, he likely would have just reviewed and approved what was written up before it was sent to the general assembly of Soviets. But he was also abit of a notorious micro-manager, so it is possible that he would have been leading the meetings where it was discussed, but so would have multiple representatives from the Ukrainian nationalists and other affected Ukrianian and Russian speaking Soviets.

Hell part of my understanding was that part of the reason the USR got Russian speaking lands was as a form of reparations for treatment under the Russian empire, though it has since been portrayed as Stalin forcing Russian speaking people onto the USR in order to control it politically. This, of course, makes no sense since the RSR already was in control of the land politically and allied with the nascent Ukrianian nationalists, and that until recently, most Ukrainians and Russians understood themselves to be 'brother-people' which has a specific word in Russian and Ukrianian. Basically, it would have required Stalin to not only understand and plan for post-Cold War Russian politics, it also would have had him understand and plan for post-WWII Soviet politics, and been explicitly against the brand of socialism that he was the leader of the faction of.