Answer: They focused on other stimuli in the room and not the marshmallow.
Explanation: They were able to distract themselves from the marshmallow, which can also be understood in the form that they were positively able to delay gratification by not eating the marshmallow, by limiting the exposure that they had to the marshmallow.
Some covered their eyes, turned around, and in general avoided any type of perception of the marshmallow to prevent eating it.
They focused on other stimuli of the room and chose to ignore the marshmallow.