export only selected audio

First, move the track view so that the track with the audio you want out is at the very top directly under the time line. 

highlight the track...then drag across the time line (on the top) with your mouse.  You should see the track reflect that "selected" area by changing color in the selected area. The time line area turns gray.
now export audio..... just that clip should come out. 

You can also do this in clip mode by selecting the clip and exporting.... 

if other stuff comes along for the ride.... it is very likely that you selected it all without realizing it.

A slight variation on a theme:

Select ALL (Ctrl + a)

Now swipe across the desired portion in the time ruler

Now Export