I think taking the drone makes sense in any foul play situation, whether a random attack, an escalated argument with other people they’ve come across or an attack by someone they knew etc. there would always be the possibility they had captured some footage on the drone that linked the person to the being in the area such as a car or campsite. Taking the drone could just be the person/persons covering their tracks
I don't think the drone itself captures any footage - from my understanding it is the actual phone that is used in conjunction with the drone that would record any data. However, I'm not 100% sure on this. Ramjet would have a better understanding, as I believe Ramjet did a fair amount of research on the drone in question.
My belief is that the foul play occurred at night time, therefore I don't see that anything captured on the drone would be a motive, as they wouldn't have used the drone yet. Just my opinion though.