Automatic Apple pay

Ok so this has happened to me on the TFL yellow card readers in London. I have my Oyster card in the back of my phone in a new card holder. Normally I have separate. So I put my iPhone on the touch in reader and Apple Pay automatically opened on the lock screen. I didn't double tap home button. And to be sure I tried it again making 100% certain I wasn't touching buttons and again it opened by itself when touched to the reader. Thankfully didn't have my finger on the home button. This happened to anyone else or does anyone know how to stop this. I'm using an iPhone 6s latest version of IOS. Thanks