1945 is before 1949.
Chinese GDP was higher during WWII than over the next several years, the actual minimum 1959 to 1961 was well into communist rule. Literally CCP rule was worse than the anarchy of civically war, it’s right up there with the insanity of Pol Pot.
This so historically stupid claim, it's not even wrong tier.
There was no GDP data under KMT - it wasn't even formally calculated.
CCP started GDP calculations, but using soviet MPS GDP accounting system that basically omitted services and lowballed production prices.
The only GDP data we have that is pseudo normalized are via estimates like Maddison project. Even they don't bother to recompose China/KMT data during WW2. The TLDR is prewar peak 1939 data (right before JP invasion) around 288B, PRC took over in 1949, GDP was 245B in 1950, grew to 306B by 1952. GLF tanked GDP from 460b to 350B... i.e. the worst case scenario of GLF floor was still 40% larger than 1950.
E: Note wiki data links to ourworldindata that pulls from Maddison and in table form KMT/WW2 data is not available and only pulling from closest data point 1938/1950 and naively extrapolating per capita. Because KMT data doesn't exist.