The other article seemed marginally more substantive. It was also submitted marginally earlier, which is what we'd use to break the tie if there was one.
There's no clearly good answer to this problem of more than one user submitting the same story. We've talked some form of karma splitting, but all the schemes get complicated, and a complicated scheme that inevitably disappoints some people is worse than a simple scheme that inevitably disappoints some people. So we rely on (a) most HN users are smart enough not to much care about karma, and (b) if you keep submitting good stories it evens out in the long run.
