Narrative magic. Writers rarely worry about numbers.
The bigger question is How was he not cooked through
He is moving through interstellar space at .5 c outside the ship.
Interstellar space is not perfectly empty. There is a thin mist of atoms, mostly hydrogen.
There's about 1 atom of hydrogen per cubic cm.
While outside the hull then as long as he's not in the shadow of the ship he's sweeping a path through space hitting the atoms in that volume of space.
Lets assume that the area of the forward facing surface of his suit exposed as he moves through space is about .5 meters square.
If he spends 30 minutes outside the hull then he'll have traveled about 15 light minutes through space.
So he'll have passed through about 135 km^3 of space at .5 c
So we're talking about hitting 1.35×10^17 hydrogen atoms at .5c
That is a very small quantity of material but it's going very very very fast.
The that's 20 megajoule of kinetic energy over 30 minutes.
At those speeds the atoms will either rip right through him as radiation or stop in his suit or inside him and produce heat.
Imagine lighting a fire and burning about a liter and a half of petrol over about half an hour with someone suspended a few inches above it.
They'd probably be a tad crispy.
Even if the ship isn't accelerating he's still screwed
There's a much bigger problem as well:
Being hit by those hydrogen atoms doesn't just heat him up and possible give him cancer, it also slows him down by about .4 meters per second assuming he weighs about 75kg.
after 30 minutes he'd be traveling something like 730 meters per second slower than the ship and is screwed.
These numbers are of course all approximate and making some naive assumptions like perfect transfer of momentum and nothing zipping through him without stopping etc but it should be in around the right ballpark.
Many scifi stories dealing with travel faster than about .1c tends to run into similar problems because it's hard to comprehend just how fast large fractions of light speed really are. These are speeds where a pebble hits with the energy of a nuclear bomb.