The correct answer is the last: "It draws attention to the image of heat's exerting pressure on things, which helps suggest discomfort or claustrophobia".
It true that the speaker is considering heat a negative force (as the third option states), but there is no evidence that supports the existence of misunderstanding.
On the other hand, the tone and phrases that the author is using, such as "thick air" or "cut the heat - plough through it" describe a situation of preassure or claustrophobia, that is even affecting the fruit. This is why she explicitly is asking heat to go away.
