yeah it could have been one panel. but it being two panels both shows us that there is distance between the caterpillars and the butterflies, and also keeps the pacing, helps with comic timing, and aids legibility of reading order. i think it's a really elegant composition

Pretty much yes, there's a bunch of different methods but mainly you're going to be introducing a "master" first which is a wider shot showing the whole scene, and then you're also using the "singles" to try to show two things at once, a frequent method for this is to shoot "dirty", having things in the foreground like the shoulder of the other actor.