Only 84 sailors and 5 officers were lost of a crew of 1000+. Possibly those killed are related to the torpedo hit. http://en.wikipedia.org/wiki/SMS_Szent_Istvan
And swimming in the Med in June when the water is 20-25 C/68-77F, and no oil in the water (Bismarck), was comfortable. Unless my eyes deceive me, are there some people running around on the turned up bottom of the ship?
The speed of the films, lapses in recording, and technical manipulations may also give a deceptive impression and the actions are not in "real time".