Q5 Pro sends DTS signal to my a/v receiver. Why?

[Machariel]

My Q5 Pro is via a Toslink connected to my AV receiver. Q5 pro utilizes a HDMI cable to connect to the TV. I'm using Firefox to stream videos from youtube. I'm using Firefox for Android because it will allow me to install Ublock Origin ad blocker.

So far my setup.
However when I listen to music videos or whatever, the audio is streamed to my AV receiver as a DTS signal. This cannot be right. Via the pc, the audio is streamed to the receiver correctly. So it's a Q5 Pro thing.

Edit: in fact, the Q5 streams all audio as DTS to my av receiver. I just opened a movie from my NAS. It's in AAC, but ends up as a DTS on my receiver as mentioned.

Anyone know what's up with this?