Viewpoint as someone whose primary job right now is recruiting: my observation on what differentiates Fine software engineers from Great ones is how they understand the problem, engage with it, and go get what they need to solve it. Fine software engineers need to have the problem pre-digested; Great ones can take ambiguous problems, figure out what's missing, and hunt it down.
I don't see the author's withholding of all problem parameters as tricky at all, but an attempt to accurately mimic the ambiguities of the real world to see what the candidate does with it.
I do interviews for my team, and I'm very aware that framing questions the wrong way quickly leads people into the trappings of their own obsessions. Be that a need for optimising the wrong things (e.g. optimising minute but easy to optimise logic next to large, network-heavy calls), or assuming the wrong perspective on a task (e.g. getting tasked with an accidentally math-heavy problem, and assuming it's about solving the math instead of their overall approach to new requirements) or simply lacking the confidence to question obvious problems in the task they were given. Interviewing is a stressful to downright dehumanising process that is hard to get right, even with years of experience.
I don't see the author's withholding of all problem parameters as tricky at all, but an attempt to accurately mimic the ambiguities of the real world to see what the candidate does with it.