Some do borrow from another picture.
.....
Secret iPhone optical zoom revealed
However, some iPhone models have two cameras on the back.
One of these is a "telephoto" lens that's preset to 2x optical zoom – no software tricks involved.
But because this lens only has one "optical" zoom setting (2x zoom), everything below 2x zoom is "digital" zoom.
So your 2x zoom image would have more detail than zooming in at, say, 1.7x.
If you do shoot at 1.7x, Apple tries to compensate by borrowing some information from the telephoto lens and adding it into your 1.7x shot.
But only the 2x zoom photo is an authentic "optical" zoom – and preferable to 1.7x.
ZOOMING on an iPhone lets you get closer to the action without physically moving – but it’s more complicated than you think. You can end up with a rubbish shot if you don’t zoom correct…
www.the-sun.com
However, I don't see how it would be possible if showing footage from another device (the drone).