Inflation isn't just a function of unemployment. Unemployment isn't just a function of inflation.
It could be that with all else held constant, plotting the two against each other would give a similar curve to the left. Or it could be that the curve on the left was presented as an oversimplification of the big picture to manipulate policy or political will.
From my pov, the ratio of money supply minus savings to goods/services supply is the biggest factor for inflation, though there's a time lag and prices are sticky downward.