I am not a teacher.
I think what this means is that we try to find out where is the person from by hearing their voice .An Indian may say the same word differently than Americans and we can easily find that out by paying attention to the phonetic details..
For example if an American say hot /hɑːt/ it would be different to someone who is from the united kingdom /hɒt/ .So these are subtle differences in the way they speak.
But we quite clearly won't notice these differences sometimes,as in example
A) Would you (/pɪk/) pick up the trash.
This is the correct pronunciation of pick as any native would speak.
B) would you (/piːk/) pick up the trash.
This could be the way a non-native English speaker could sound like.But the pronunciation given here is for Peek.
we have overlooked the subtle difference in pronunciation,though it was clear to us it is not pick it is peek in the second sentences.From the context we have recognized that the underlying "i:" sound in B should be "I" sound.
Hence we have overlooked the subtle difference though we have recognized the speakers mistake in B.As the "i:" sound does not fit the bill in that context and "I" sound is part of that word pick our mind has replaced it automatically because it "I"
is part of the word pick not "i".
BTW I believe this a sentence from "The Study of language".
In nutshell our mind may not pay attention to the phonetic details if we know what the word in the context is.So even if I say pooock up the trash or piiiick up the trash ,our mind would register pick up the trash.
Context matter more than phonetics.
we have not only disregarded that difference b/w "I" and "i:" but also recognized "I" sound for "i:" because it is part of the word pick.
This is my opinion and I am not a teacher.
Student or Learner