It’s an element but more than plausibility. Inspection passes to unimproved sites are in large part an effort to determine the plausibility of a landing there. For that matter, so is an attempt to test the winds when there’s a strong wind.Is this what you're talking about: "Further, the law judge determined that respondent has the burden of proving that his low altitude operation was necessary for takeoff or landing, and citing respondent’s testimony, the legislative history of the regulation, and Board precedent, found respondent failed to meet this burden given that the landing site was inappropriate under the circumstances."
Seems like the whole case rests on whether or not Trent could plausibly have landed there. The judge determined that he couldn't. Trent claims he could.
The legal precedent (Court of Appeals, not just NTSB) talks about the “appropriateness” of the landing site. In one Court of Appeals case, the pilot was violated at an airport because the approach (and landing) was to a taxiway rather than a runway, passing within 500’ of people.