I'm not concerned about this. Like they said, it's more of an elaborate "Alexa butt-dial."
For those who are concerned, just disable calling from Alexa. Similarly if you are concerned about butt-dialing on your smartphone, don't put your phone in your back pocket. There are always going to be possibilities of activating functions unintentionally, whether by voice, by an errant press of a button or screen, or something else. Years ago I had a touch-screen monitor for my computer that was clicking things on the desktop because a fly was crawling on the screen. It was an older screen that used optical sensors instead of pressure or capacitive sensors. If I wasn't right there in front of the computer watching this happen, I might have thought I was hacked and someone on the outside had control of my computer.