S9 dialing immediately after locking the screen?

[OilMagnate]

I've been noticing a trend I do not like. If I'm texting someone and lock the screen to put the phone in my pocket to resume the conversation later, it will sometimes vibrate and dial the person I'm texting. If I don't feel the rapid, subtle vibration, my pocket ends up talking to said person. What is causing this? I usually lock the screen, literally gently flip/toss the phone into my right hand and then slide it into my right pocket. I don't think it has anything to do with the fingerprint sensor, because when my right hand makes contact with the back of the phone, the only part of my hand that touches the sensor area is the joint area of my thumb (better conveyed in yellow in this pic):

So if it's not the fingerprint sensor unlocking it, then is there some sort of 'shake to call' feature I'm unaware of? I've tried re-creating it hundreds of times over many months. It definitely only happens when my phone 'hits' my right hand (gyro sensors?) after I lock the screen with the messaging menu open. I'm not pressing a 'dial' button, or anything on-screen. It's definitely something impact/shake/gyro related or possibly fingerprint sensor related (not sure how it would even be possible). I'm trying to break the habit and learn to close messaging before locking to avoid this, but it's incredibly infuriating. I've always put phones in my pocket this way, and I've only had this issue with the S9. I understand I've already answered my own question by breaking the habit, but any tips are appreciated to stop the dial feature.

 

[mk378]

On my old Motorola with Android 8 the drill was to push the side button to turn the screen off (but don't put it in your pocket yet, it's not really locked!). Push the button again to turn the screen back on and then hit the lock icon at the bottom center. Now it's locked. A message should come on "Phone will stay locked until you manually unlock." That means with the PIN or fingerprint.