Yes, I was having a conversation with wifey last night about that very thing, how instead of 'Uncle' referencing a direct relative, it was also sometimes used by some mothers to their children to describe their latest fancy man.
On the 'Auntie' as a racist connotation though, I was honestly unaware, I'd never given it any thought, but wifey as an (ex) teacher was.
It's claimed that during US Slave times, many of the owners of said unfortunates would never refer to married slaves in their ownership as Mr & Mrs as it would possibly give them the impression that they were on a level with the owners, so instead they would be called Uncle & Auntie.
As others have said, it seems a very American thing though, certainly many Asian sub Continent familes use 'Auntie' and 'Uncle' very much as a term of endearment for respected members of their communities.
However, in the light of this now, I do agree that the claimed employment of 'Auntie' regarding Abbott as reported in the document does seem somewhat questionable. There just doesn't seem to be any reasonable explanation for it in that context except an element of casual racism.