These are two good questions, Sue. I can understand your confusion.
1. It is possible to say 'was born' here, but the past perfect is more accurate. Here's why:
If you say 'He flew back to the pond where he.......', and the next clause is also in the past simple, we would assume that this second event occurred AFTER the first. For example 'He flew back to the pond, where he met his family again and lived happily ever after' . (It's a non-defining clause now).
If you use the past perfect, however, it makes it clear that this event happened some time BEFORE the event referred to in the first clause.
2. This is wrong in British English, but acceptable in American English.