Most BT speakers have a battery, which means it has to be in carry-on luggage. Why it would be powered on is the question, but this could have happened inadvertently by getting knocked around in a bag.

I do, because I want to listen to music when I travel. Not in the plane, but at my destination.

If you want it at your destination you are kind of forced to as you can't transport batteries in your checked luggage.

Speaker in carry on luggage to be used in vacation. They were flying to Malaga

"bare beating"