Why should Payne have been a coauthor of Russell's paper? It was (so far as I can tell) entirely independent work on the same question. She deserved a citation

Why should Payne have been a coauthor of Russell's paper? It was (so far as I can tell) entirely independent work on the same question. She deserved a citation (which she got) and acknowledgement that she had got numbers very similar to his (which she got), but you don't make someone a coauthor just because you and they are working on the same problem.