What happened when Jonas's number should have been called and how did Jonas react in The Giver?

When Jonas’s number is called, he is skipped.  Jonas thinks he has done something wrong and is embarrassed. 

The Ceremony of Twelve is the most significant day in a child’s life.  It is the day he takes the first steps to becoming an adult, because he receives his assignment.  Children in Jonas’s community do not choose their own jobs.  The community chooses for them. 

Jonas has no idea what his assignment is going to be.  The children are closely watched by Elders for the years leading up to the ceremony.  The Elders review their volunteer hours and talk to their teachers.  They base the assignment on each child’s abilities, intelligence, and interests.  Jonas has not concentrated his hours in one place. 

When it is Jonas’s turn at the ceremony, something extraordinary happens.  All children born in a year are assigned a number.  Jonas is number 19.  However, the Chief Elder calls number 20 after number 18. 

She skipped me, Jonas thought, stunned. Had he heard wrong?  No. There was a sudden hush in the crowd, and he knew that the entire community realized that the Chief Elder had moved from Eighteen to Twenty, leaving a gap. (Ch. 7) 

Jonas is embarrassed and confused.  The only case where a student would not be called is if he did not complete his volunteer hours, and this would be a cause of great shame for the child.  Jonas does not think this is the case, and he is horrified.  In a community where standing out is considered the worse thing possible, attention has been called to Jonas in front of the entire community. 

Jonas hopes that she has made a mistake as she continues to all of the other students.  After the last one, she acknowledges the unease in the crowd by apologizing.  She also apologizes specifically to Jonas for causing him anguish.  Then she makes an extraordinary announcement. 

"Jonas has not been assigned," she informed the crowd, and his heart sank.

Then she went on. "Jonas has been selected."

He blinked. What did that mean? He felt a collective, questioning stir from the audience. They, too, were puzzled.

In a firm, commanding voice she announced, "Jonas has been selected to be our next Receiver of Memory." (Ch. 8) 

This is a puzzle to Jonas.  He is only vaguely aware of this job, and has no recollection of anyone being selected for it.  He is told it is a great honor, and he was chosen because he has special traits the community needs, such as intelligence, integrity, courage, wisdom, and the Capacity to See Beyond.  He does not really know what that last one means, but is aware that he does have it because he has strange visions.