Back in the early days of football, players would bring their own tops to wear and these would be jerseys or guernseys. A guernsey would be a fairly heavyweight jumper, traditionally worn by sailors, and so preferred by goalkeepers. A jersey is lighter weight but would still have typically been wool.
This evolved into players bringing their own shirts, as they were lighter still than jerseys, and so you can see in some pictures from the late 1800s that some players had half-button shirts and others with the full button design. This is because they were literally the shirts that the men would have worn to work during the week.
In the early days of international football the players wouldn't be given a shirt when they played for England, but would be given a badge to sew onto their own shirt.
The name guernsey stuck with Aussie Rules as the shirts are sleeveless and so it marked a difference from the jersey worn in football and rugby, even though it bares no resemblance to an actual guernsey jumper.