The best interpretation of the most likely cause of the outlier in the scatterplot titled "Sweater Sales by Temperature" would be:
There is a one-day sale on sweaters on a warm summer day.
This option suggests an unusual spike in sweater sales that does not align with the general trend related to temperature, which is likely leading to the outlier. On a warm summer day, we would typically expect fewer sweater sales; however, a specific sale could create an exception to that pattern, resulting in the outlier.