I couldn't agree with the comment by Michael Galuza on my answer to Algorithm to answer existential questions - Reduction, but I can see that if the question is "is my understanding right?" and my answer is "yes", then the answer doesn't add much value to anyone who may (very reasonably) have doubts about my qualification to comment. In this case, the OP had done all the work, so there was nothing more to add - all I had to do was to read the paper she was concerned with and convince myself that her reading was correct. Any thoughts on this would be appreciated.
I disagree with quid's answer. Many questions end up unanswered because people take this approach and answer such questions in comments. Of the two risks of leaving the question unnecessarily unanswered on the one hand and answering only the question without giving unsolicited additional information on the other hand, the former weighs more heavily in my view. If the OP had wanted further information beyond confirmation, they could/would/should have asked for it.
Certainly one should pause to think about what one might add to make the answer more useful, and point out small errors or possible improvements in the presentation being confirmed (and apparently in this particular case there was an opportunity to do so), but if none come to mind, one should simply answer the question as posed, and one should also not feel deterred from answering the question as posed if one doesn't have time to search more intensively for improvable details.
Such a question is similar to a proof-verification question. I wrote up my opinion how one should answer those in some detail at How to answer proof-verification questions?
In brief, I think normally more detailed answer can and should be given. A simple "This is right." should better be given as a comment.
Such detailed answers can include:
- Giving a high-level summary of the argument.
- Highlighting points were details are omitted.
- Putting the argument in a larger context.
- Suggesting alternative arguments.
More details on my opinion around this can be found at the linked to question.