The focus depth won't necessarily be endless, as you image, it will however, be greater when focusing on distance subject matter. The main reason is because you never use a drone for close up photography. Virtually ALL drone photography will be...
In such cases, I can understand the need to go higher. With that said, why not simply start on top at, as you put it, ground level. Which go down into a canyon that you will need to fly out of, in the first place? Seems a no brainer for me.
Saying "Tons", is a standard British saying. Those who are not British would not understand the use of that word, in this context.
In the USA they may say, down in the south... A mess O' as in, "a mess O mosquitoes came flying at us". In...
But since all we know of the video incident is that the drone had a problem and was lost, all of those people were guessing and assuming as you've done.
You imagine ... your own personal guess ... that says it all.
That one drone was lost...