Definitely a few slightly more forceful reasons why people get tripped up by this.

1. Group voting tickets were only abolished 4 federal elections ago, and are bizarrely still a thing here in Victoria and Melbourne City Council. So, people’s belief in this is not totally irrational, but likely carried more by lore than facts.
2. Many folks look at elections as a chore rather than a precious gift. They would rather remain ignorant about how they work. “Don’t vote for candidate X because they just send their preferences to candidate Y” is more of a meme (in the broad sense of the word) than a well researched political opinion.
3. There are people that benefit from stoking uncertainty and confusion about the Australian election process. Many of them are not Australian citizens. Just look at the AEC’s Twitter “Replies” tab. Cookers and Russian agents.