It seems like it is incorrect because it is using a general term instead of a specific term.
I think that the logical conclusion, for the first statement, would be that all the tulips in the garden were tall tulips.
Just like the second, it should be that the only gorillas in the zoo were small gorillas.
I also think it has something to do with the misconception that the terms are interchangeable.
A plant is a broad term that contains many sub-categories, while tulips are a specific reference to a type of plant.
I could be wrong, and heck... I probably am wrong.
This is quite a difficult example.
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