Another way to describe this could be that the meaning here is inherently ambiguous between "is-a" and "has-a", but the puzzle only makes sense (and only has a solution) if you interpret as "is-a".
In Mystery Hunt puzzles, which this originally was, "we have to interpret this in a way that would allow there to be a meaningful and unique solution" is not only a perfectly legitimate form of reasoning, but often necessary!
It's not really exactly the same kind of reasoning, but in a puzzle I wrote a year before this for the same event
https://www.mit.edu/~puzzle/2012/puzzles/into_the_woodstock/...
you could look at it and say "hiragana is only ever allowed to be used to write Japanese!!!" but insisting on that rule (much as it applies in most situations) wouldn't give the puzzle a meaningful solution. :-)
Maybe a closer equivalent would be that in this year's Mystery Hunt, there was a puzzle using a set of variant Hashiwokakeru (Bridges) logic puzzles. There were hints about which rules were changed but it wasn't stated whether the rule changes applied individually (one puzzle each) or cumulatively (when rules get changed, they don't change back afterward), or some other way. So, it was necessary to make assumptions about what was meant and see whether they allowed a solution. That's typically considered fair and appropriate throughout Mystery Hunt-land.