Considering the fact that this video was made in 1964, (which is when the memories of WW2 and the censorship of Japanese media with patriotic propaganda during WW2 was still fresh in people's minds) I believe that Tezuka's aim was to try to show people that what he illustrated in the short animation was what happened in Japan during WW2.
By the way, this short animation reminded me of a music video by A-ha, a Norwegian band from the 80's. Please take a look, I guarantee it will remind you of Tezuka's animation. (The quality sucks so please watch the better version on the actual YouTube website)
