After Nuk speaks about how she really feels, Obi then reassures her that there really is nothing to worry about.  
From what he knows, he is sure that they’ll be as accepting to her as they were to Obi.
 
(I mean, if they accepted an entire ELEPHANT into their community without a problem, then I’m pretty Nuk will be just fine.)
 
Nuk is still a little hesitant, but Obi, being the friendly, reassuring Elephant that his is, asks if he has ever betrayed her before.  
With a short moment of thought, she realizes that Obi never really did go against anything he told her since meeting him.
 
If you’re wondering when they actually met each other, it was when they were both very young.  
They were both just about the same height as well!