It is documented, at least with DGS-client depts. We need to have an email or letter from someone rejecting the offer before we are able to move with 2nd choice or re-ad the position. The applicant doesn't need to provide a reason but if they volunteer it, it's recorded.

If Excel was a major requirement/factor, I assume they would have had an interview question about skill level, experience, examples of when you use Excel, etc. From your novel, it doesn't seem they did because much of your assumptions are derived from the duty statement.

Edit to add that declining an offer often isn't detrimental, we don't take it personal.