"A" Chinese space station is perhaps the more intriguing part of that headline.

Unique strains of bacteria in confined, isolated places presumably happens a lot. Space stations don't undergo mitosis nearly as often.

So if it turns out they evolved on the space station, would that mean we discovered extra-terrestrial life, or is that cheating?

It wouldn't count in my mind because it's not life that originated off the Earth. It just mutated off the Earth.