Maybe just sloppy title writing.

Because TFA says nothing about it growing outside.

“New research being presented at the Astrobiology Science Conference shows the International Space Station has an irritating mould problem — not only on the inside, but the outside, too.”

"We now know that [fungal spores] resist radiation much more than we thought they would, to the point where we need to take them into consideration when we are cleaning spacecraft, inside and outside," Cortesao said in a statement.

emphasis mine

I'm not quibbling about "outside". But nothing like "grow*" appears there. Spores aren't actually growing. Just waiting for suitable growth conditions.

Ah, apologies for not picking that up.