Some fungi can survive the conditions of space, which is pretty incredible. I think that’s basically it.
It is literally incredible, and the title is misleading.
The fungi was in some kind of box that was filled with a lot of CO2, a little O2 and H2O, and other stuff to simulate the atmosphere on Mars.
That box was then placed outside the space station.
It wouldn't survive if it was just growing in space, outside the space station. Believe me, I'm outside of it right now and it is not going to be fun[1].
1: I'm about to start doing my taxes-- blecch-- here on Earth, which is technically outside of the space station.