how?

When you write a kata together, I think you should mention it in a footnote or in the comment section, to avoid any discussion. Also, why not try to come up with a different solution, as an additional challenge?

Please explain how you submitted the exact same solution as the kata author's solution. This really shouldn't happen since the task is far from trivial one-line: so the most likely explanations are that either you're a sockpuppet, or you're cheating, or you're colluding with the kata author, which are breaking the site rules in either case.

(Also, upvoting your own solutions and comments would be obvious vote manipulation, which also violates the site rules.)