Benji concludes that there are only red and blue chips in the container. He does choose two numbers that add to 20, but the numbers in his estimate do not appear to be related to the number of each color in his sample. He may not see the relationship between the number of chips in his sample (10) and the number of chips in the jar (20).
Sasha doubles the number of chips of each color in her sample to predict the number of each color in the jar. She sees that since the number of chips in the jar is twice as much as her sample, it is reasonable to double the number of each color from her sample.