When I was a little kid, I got a nosebleed while being watched by a family friend for a little while.

My parents had - correctly - always told me to tilt my head forward when it happened, but this family friend was extremely confident that I should be tilting my head back.

About an hour later, I wound up throwing up a significant amount of blood, as my stomach rejected all of it that had drained down the back of my throat.

They came home, fixed everything up, and then made sure that she knew not to have a child tilt their head back during a nosebleed.

I'm not really sure why people think that tilting back works better, but at least it isn't a common thing (in my experience.)