why does the poet say she has nothing to do with explosions?

The speaker seems to be disappearing, which becomes evident in the previous line, "As the light lies on these white walls, this bed, these hands." As you can see, she doesn't refer to the hands as her own....... but rather as "these." In the specific line you're questioning she says, "I am nobody; I have nothing to do with explosions," which leads us to believe that in this cold, wintery room (literally and emotionally) she has detached from the world around her. The mood is cold and unfeeling.

I believe the explosions can be looked at in terms of of the first lines. The tulips are described as exciteable. The narrator herself might also be described as exciteable, as in line three she tells us that she's learning peacefulness. The operative word, learning. From this we know she's not a naturally peaceful person.

Tulips rise unbidden, often they bloom too early because of the fair weather that comes for a few days, tricks them, and then reappears. This explosion of the tulip bulb just might reflect the narrator's explosion of emotions, the explosions she's "learning" to be peaceful.

We aren't directly told what the explosion is, but the above explanation is my interpretation.