The two actions are blended together. After the Pull By, the dancers don't stop and form a couple, and then separately do a Courtesy Turn. As soon as they get past the dancers from the other couple, they put their left hands forward and the dancer on the left reaches out to put his right hand on the back of the dancer on the right, for the Courtesy Turn.
A common mistake is for the dancer on the right to turn or drift to the right after the Pull By. This is because she was just going around a dancer to her right. If she were doing only a Pull By she would need to adjust slightly to her right to be back-to-back. But if she isn't careful she may go too far in that direction. In the context of a Right and Left Thru, she needs to anticipate the Courtesy Turn, by being ready to join hands with her partner and start turning to the left.
Note that each couple ends facing the opposite wall from when they started.