Audio/video and volume
 

Hi: I have a 2017 NX and had a question. I previously owned a 2010 RX so I'm making comparisons between the two.
Wondering if this is as designed: if I have my cell phone (iPhone) connected to Bluetooth and lets say I browse and click on a YouTube or Facebook video, it plays fine. But when I raise or lower the volume, the music player (from phone) starts automatically instead of raising the volume of the video. I've tried this with phone connected with a cable as well as via Bluetooth. Am I doing something wrong or is this as designed?