I'm wondering if Carl August might have been the father and him and Clara took him in and registered his birth as a late registration in 1928 and put their names on it?? Probably was easier than admitting what happened and or adoption. I have lots of scenarios running through my head

I think if the OP wants to look into it more both birth certificates might have to obtained and hopefully shed some light onto it.
EDITED TO ADD.. Stella would have only been 15 when she had Stanley.
Brief Life History of Stella May
When Stella May Pressler was born on 18 January 1907, in Burra, South Australia, Australia, her father, Ernest Auguste Pressler, was 36 and her mother, Sarah EAST, was 34. She married Percival John Coombe in March 1924, in Broken Hill, New South Wales, Australia. She died in 1998, in Broken Hill, New South Wales, Australia, at the age of 91.
https://ancestors.familysearch.org/en/LCQD-3HS/stella-may-pressler-1907-1998.