Yes, but I think that Ironside wishes to claim that Poland's suffering was unique in scale, i.e. that the scale was the largest ever. It's a highly disputable claim (Ukraine lost a similar percentage of its population in WWII and Belarus lost a significantly higher percentage, with Ukraine also losing some four million before WWII during the Holodomor) and one which adds precisely bugger all to useful discussions.
If anybody is interested in reading about the events which took place before and during (and after) WWII in the this area, I very much recommend Bloodlands by Timothy Snyder. Here's an excerpt from the preface:
This is a history of political mass murder. The fourteen million were always victims of a Soviet or Nazi killing policy, often of an interaction between the Soviet Union and Nazi Germany, but never casualties of the war between them. A quarter of them were killed before the Second World War even began.