It's a bit silly to chase down original authorship of an idea that is a minor detail visible to many people who work in a field.
It's like asking who was the first person to discover that all multiples of 11 have the same parity in the respective sums of their odd and even digits.
The proof follows from this instance of the discovery, with an Oklahoma U student indepently discovering and an OU professor indepently proving. I think that's a perfectly reasonable way to track what happened.
I am unable to open the pdf or follow any of the links from the wiki talk page, so the proof may predate this instance, which would invalidate my point.
Sorry, can't edit the comment from here, those italics make it seem snarky. Should have been an asterisk after proving and before the next sentece that I forgot to escape.
Since there had to be a first person who discovered that all multiples of 11 have the same parity in the respective sums of their odd and even digits, that question is obviously interesting to some historians. Due to what circumstances was that person first? What hindered others before that person? How long was the lag before use of decimal and the discovery?
It's important to remember that while technically there is a chronologically first person to discover X for all X, that doesn't imply that that person is the only person to discover X. For sufficiently obvious X, there are likely to be many independent discoverers and highlighting the chronologically first one heaps praise somewhat arbitrarily on one of them.
Making a discovery in mathematics confers a kind of immortality. You're part of a conversation that has lasted centuries and will continue for the life of mankind.
It's like asking who was the first person to discover that all multiples of 11 have the same parity in the respective sums of their odd and even digits.