Have the snooze buttons on the iPhone changed?
It looks like this has been around for a while.

I found an iOS 10 user complaining that the Home Button shut off the alarm:


  turning on the phone (pressing the home button) shuts off the alarm!


(Source)

I also found several articles form a while back explaining you can use the Home Button to stop your alarm. 

Just tested and the Home Button also stops it for me. 

It could possibly be you thought you pressed another button that you didn’t, or maybe you were using another app or jailbreak tweak.