How do you know that it is "a" step rather than "one" step?
You don't :). But "one step" instead of "a step" means that the number of steps is stressed I suppose: Spelaren tog ett steg and that's normally not the case.
Maybe "one step" is accepted as well. Have you tried it?
It wasn't, but that's okay. What you say makes sense.
I just added it, so it'll be accepted in the future.