Confidence Interval for population mean ( Small Sample)

Question Statement:

The distance traveled, in hundred of kilometers by automobile, was determined for 20 individuals returning from vacations. The results are:

12.5, ............, (all the 20 numbers are given).

I am asked to calculate the 90% confidence interval for the population mean.

The instructor calculated the mean and the standard deviation, using the 20 numbers given, and he said that these are the population mean and population standard deviation. Then he calculated the sample mean and sample SD from those values. Is he correct ?

I think the mean and the standard deviation of those 20 number are already the sample mean and sample SD.

This is the only issue I have, I know how to work out the rest of the problem.