That's an exaggeration and regionally specific NSW and QLD it's common for jumpers and jackets to come out on mid to high 20s. In Tasmania and Victoria shorts in 10C is not uncommon.
Also light jackets and long sleeve shirts are not uncommon in summer especially if working outside. Because the higher UV levels are a real killer (literally). Even with sun screen you can feel the burn very quickly.
I live in NSW and I've seen people wearing shorts in winter but nobody with a jacket if it's 30. Long sleeved shirts for workers, yes sometimes. Umbrellas, yes, too. I didn't know jackets were a thing for hot QLD days.
The sun is hot and stings as you say though, granted