I think the point of the parent comment was that simply being in a cold vacuum doesn't make you instantly cold. That still requires a process of heat transfer, which occurs in a fluid via conduction, convection, and radiation.

When immersed in a vacuum the conduction and convection heat transfer paths are sharply reduced, so the question then becomes how fast do you cool off via radiation alone?

I'm not a physicist so I don't know, but it's certainly nowhere near as fast as conduction/convection (in fact I believe heat dissipation was actually problematic for many spacecraft designs).

As it turns out, even on earth's surface, radiation is a more efficient heat transfer method than conduction and convection through the air. Objects under a clear sky quickly drop below air temperature in many circumstances.

Thank you! I did an hour jog tonight, and most of that time was spent trying to figure out why there was frost on the ground with an air temperature above freezing and a warm breeze.

I wonder if heat might also be conducting downwards to the frozen ground below.

What he's trying to say is that if you toss a rock into liquid helium or a 4 Kelvin zero g vacuum it's going to get colder faster via direct contact with the helium than via radiation in the vacuum.

Wow, that seems amazing but now that you mention it I think I've heard of that happening even in deserts.