Approaching this specific answer
I think you've nailed it with the word 'appropriate'. For ninety-nine out of a hundred questions, I would (personally) say that the approach you are highlighting is not a great hermeneutical method to apply in the first instance, and the answer applies very few of the tools we expect to see in most high-quality answers, and is far more theologically oriented.
However, in this fairly unique case the asker literally specified that they were interested in approaching the problem using "reasoning by transitivity", and so I'd personally say the answer in question does apply this approach well. It's always appropriate to seek clarification and supporting evidence on Answers, and so the helpful thing to do here would be to be specific about what you feel is critically missing from the answer. "Opinion only" isn't really helpful feedback for anybody, and is more likely to build strife than be helpful for most.
Approaching answers we don't like
It's tricky sometimes to approach questions and answers impartially - we all carry our own traditions, cultures, beliefs and preferences, and too often (all of us!) insist that our own way of thinking is the norm others must conform to, or unfairly penalise others for simply diverging from that. I think we've all been on the sharp end of such attitudes, and so it's something each of us has to fight somewhat. And so I sometimes find myself trying to consciously tread that line between "where does this answer clearly need more rigour?" and "where is somebody just approaching this from a different cultural perspective?"
I personally try to upvote good answers and downvote less useful answers (with helpful commentary where possible), but do also counter-balance that with a special care for those who are clearly approaching hermeneutical problems from different cultural viewpoints.
Where it gets complicated
I know you haven't asked about the question, but these thoughts feel relevant:
One of the long-term challenges on BH.SE is that we've had an unfortunate history of Stump the Chumps questions, where users design questions so specific as to lead to only one possible answer. Many experienced users are rightly cautious of questions that look like this, and it wouldn't take much for the Question you've highlighted to tip into that category.
This is clearly a theological question, though posed in a hermeneutical way that at least appears to be seeking different views. It's likely to attract theological answers, though hopefully only the highest quality answers with sound hermeneutical grounding will receive the highest votes. Sometimes it can be confusing when near-identical questions can be treated quite differently. In this specific case it does seem that though the user is interested in this specific method and clearly has a preference for the answer (don't we all), they are still open to different views, and so it wouldn't surprise me if this question could have a few different highly voted answers from different perspectives.
We've got such a varied community that it's impossible that every Question and Answer ultimately gets handled impartially, and so it can be a little circumstantial as to which Q's and A's get upvoted, downvoted or closed. For this reason I'd again emphasise the importance of helpful comments - DV's and Close votes should always be something we're willing to change if the author can provide better detail, and that feeling of 'helplessness' that users will DV or Close vote us regardless of what we do is part of what can engender hostility in the community.
If in doubt:
Blessed are the merciful, for they will be shown mercy. (Matthew 4:7)