When a single page drops and the rest of the site holds, the isolation itself is the message: the cause is page-specific, not site-wide. If an algorithm update or a technical fault had struck, the damage would not respect the boundary of one URL while leaving its neighbors untouched. The pattern of one falling and many holding is observed behavior that points the diagnosis inward, away from the whole-site explanations that fit a broad decline.
That reasoning works by elimination. Site-wide causes act on shared things, an algorithm re-weighting the domain, a crawl or index problem, a template or server change, and those effects spread. When the rest of the site keeps its positions, you have direct evidence that the shared layer is healthy. Whatever moved this one page did not move anything it shares with the others, so the answer lives in what is unique to that page.
Once isolation has narrowed the field, the realistic suspects are short and all page-level. The query’s intent may have shifted, so the page now answers a question searchers have stopped asking in that form. A competitor may have published something that simply outdid this page on the same SERP. The page itself may have been edited in a way that weakened it. Or it may have lost a key link that was carrying part of its authority. Each of these touches one page without disturbing the rest, which is exactly the shape you are seeing.
So the interpretation is concrete rather than ominous: an isolated drop is a page-level event, and that reading shrinks the suspect list from the entire domain to one URL and the SERP it competes on. Reading it instead as a site-wide update sends you auditing healthy pages while the real cause sits unexamined on the one that fell.
For the page that dropped, examine its specifics: re-read the current SERP for intent change, compare it against whatever now outranks it, review its recent edit history, and check whether it lost a meaningful inbound link, rather than auditing the site that is plainly fine.