GP said they were in Sydney. As far as I know, the week officially starts on Monday in Australia. That's also the case for most of Europe, BTW. Maybe their locale wasn't set right or it's another case of American software assuming weird American standards for the rest of the world.
I didn't know this about the USA - but it's still called 'the weekend'? (GP uses it at least) ..Even though 50% of it is apparently 'the weekstart'?
Yes, the weekend is Saturday and Sunday in the United States. I guess you could consider it like "bookends", for us it's the start and end of the week.