The focus of the series on video material unfortunately introduced ideas from Nazi pseudo-documentaries. This comes up in episode 2 "Lightening War", where Polish cavalry is mentioned in contrast to Nazi motorized warfare.
This is a paragraph from Wikipedia article on the subject:
Nazi fake newsreels and forged pseudo-documentaries claimed that the Polish cavalry "bravely but futilely" charged German tanks in 1939, and that the Polish Air Force was wiped out on the ground on the opening day of the war. Neither tale was true (see: Myths of the Polish September Campaign). German propaganda staged a Polish cavalry charge in their 1941 reel called "Geschwader Lützow".