Some other senses of the words than the ones you found are most relevant. Here's what stands out most clearly to me (native AmE):
man: an adult male human.
drone: a male ant, bee, or wasp.
bison: a buffalo.
bull: a male cow.
So, bison stands out as the only one that doesn't mean the male of the species.
The word man also means a human of either sex. English has a number of words like this, where one sense of the word fully encompasses another sense. For example, humans are distinguished from animals, but also humans are a species of animal. A drink is a serving of any beverage, but a drink is also specifically an alcoholic beverage. When people say rectangle, they usually mean a shape different from a square, but in another sense, a square is a rectangle with all four sides equal. Somehow, these ambiguities seldom cause confusion.
One reason this question is pretty easy is because even though man has a generic sense that includes both sexes, it's a secondary sense of the word, in addition to being fairly rare today due to attempts to remove sexism from English. The primary sense has always been "adult male human".
By the way, usually the word for the male of a species also serves as the generic term for both sexes of that species: for example, lion, peacock, boar. The only exception I've ever heard of is cow: cow primarily means the adult female of that species, just as man primarily means the adult male of our species, but cow is also a generic term for any animal of that species regardless of its sex or age. This might be one reason why bull drew me into noticing the male senses of the other words. Also, bull is the name specifically for the male of many species; here is a big list.
A note about salience
By the way, this would be a terrible exam question, because other answers are also reasonable. For example, man is the only human; the others are animals (non-human animals, that is). Luke Sawczak's comment provides other reasonable interpretations, and Peter's answer gives two more. My explanation above tells how the maleness of three of the senses became most salient in the mind of one native speaker.
Awareness of what is most salient about words is crucial for communicating, since that's what guides your listener's attention to what you want them to see or think of. My main point here is that maleness is extremely salient in the words man and bull—the latter especially just after being primed by the word bison to think of animals. That tends to make the male sense of drone more salient, when normally it wouldn't be. This won't work the same way for all fluent speakers, but I'm sure it's very common. Many native speakers, especially if looking at this question casually or quickly, might not even notice that other answers are also just as reasonable.