Have the snooze buttons on the iPhone changed? For as long as I can remember, I’ve been snoozing my iPhone SE’s alarm by pressing a button on the phone. As far as I can remember, any button would do - home, volume, on/off. 

Now, if I press the home button when my alarm goes off, it turns the alarm off completely, instead of snoozing it. The other buttons still snooze.

Has this actually changed, or am I just losing my mind?

iOS 12.1.2 iPhone SE.
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.