The first thing we will do is define the linear regression:
In statistics, linear regression or linear adjustment is a mathematical model used to approximate the dependency relationship between a dependent variable Y, the independent variables Xi and a random term ε.
For this case, the linear regression line is:
y = 0 (x axis).
It is a good model because the points of the scatter diagram are all very close to the x axis.
Answer:
The regression line is a good model because the points in the residual plot are close to the x-axis and randomly spread around the x-axis.