The thesaurus isn't being helpful in this instance. Does this make sense? Bill zoomed the image out and turned it into an aerial view. I usually think of a view being zoomed as something getting closer not further away. "Panned out" might work but I'm not crazy about that description either.
I think "zoom out" is totally normal? It doesn't sound unnatural to me anyway. I'd say "zoomed (object) out" is a bit awkward, only because it splits the verb phrase up in a way you don't hear too often. I don't think it's incorrect technically, but to me "Bill zoomed out and turned the image into an aerial view." sounds a lot better. Just my $0.02.
I do not think there's an antonym. It's zoom in/zoom out. I think that what you wrote works well, but if you don't like it, then maybe try to use some words that describe the "zoom out" action, like "decrease, reduce, original size"? Nah. I think that zoom out works better. Too much blah otherwise.
I tend to agree "Bill scrolled his mouse wheel to zoom out, then clicked on aerial view" - the root of the phrase is from zoom a lens in or out in photography. I wouldn't use downscaled because that generally means to reduce the resolution (ie the number of pixels in an image) rather than to zoom out for a wider view
