Please read the transcript for reference.
I’ve already heard stories about her grandfather. He was from Scotland; he was a sailor, but not a very good sailor, so he only got as far as Portsmouth, a big navy town on the south coast of England, not very far from Scotland at all.
The bold part seems like an essential phrase to me. Since removing it should not change the meaning, let's see
He was a sailor so he only got as far as Portsmouth.
Then the last two phrases are also non-essential so I avoid writing them. I think it should be like:
He was a sailor, but not a very good sailor so he only got as far as Portsmouth.
A similar one from the same:
But I know that her mum was from somewhere that was Germany , and then became Poland, so she’s really German, I suppose.
Again the bold part seems to be essential to me.
What do you think about these construction?