I don't know, their science is legit. Apparently humans can stay alive in the vaccum of space for like 15 secs.... you'd need to avoid solar radiation, and pebble like debris flying 100mph of course. Your lungs would burst after a few secs too if they had any in them...thst gives you roughly 15 of oxygenated blood b4 you passout. The cold doesn't kill you right away because an objects heat doesn't diffuse (losses) as quickly in a vaccum as in an atmospheric space. Bleeding out for bursted eyes is the most immediate concern.
Naomi's face got burnt on the side that was facing the sun. She exhaled as the doors opened. That shot was full of oxygenated blood. Her eyes we beginning to bulge out her face. The books talked about the belters having a sense for space walks and zero movement.
If anything, old dude should've had enough time to close the doors before he died...unless he did exhale and his lungs blew up.