The tanks depicted rolling on the wheat field are German Pz III Ausf D, which are correct to the date, but alongside with them are some StuG III Ausf G tank destroyers, which were not produced until late 1942, more than two years after the events of the invasion of France. Though could seem that two years are not relevant, the StuG III are at least three generations more advanced that the early tanks available in 1940 so this would be similar to show machine guns in the American Revolutionary War or modern F-117 or F-22 fighters in Vietnam War, as examples.