This particular map is the territory claimed by the then still newly-minted Ukrainian state. Basically the then-current Ukrainian equivalent of the likes of Greater Serbia, Greater Hungary etc.
There was no border in those territories for so long, anything they could have drawn wouldn't really have any meaningful historical connection. So IIRC they went by the Russian Imperial demographic maps and claimed most territories on those showed >25% "Malorossians". Ironically, this ended up pilfering some territories from Belarus, as well - note where Pinsk is on that map!
It's kinda amusing what these people are bashing current Russian maps with Kherson, yet they are fine with a postcard as the evidence of.. expansive borders.
That's 14 years before 1933, and the border was not there by then, but...