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I am surprised that it survives twitter's image compression. I'm not familiar with JPEG format, but I'm familiar with PNG. I guess it's using some zlib-compressed EXIF-like metadata field, seeing as ZIP also uses DEFLATE/zlib/whatever?

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It's embedded within an ICC colour profile, and therefore doesn't get touched by any image compression/resizing logic.

Some eager image compression techniques will strip metadata including profiles (e. g. ImageOptim: https://imageoptim.com/color-profiles.html) But generally you are correct.

any image compression/resizing logic [in twitter.com] [in 2018]

How would do that nicely and automatically, to do funny things like that in a way that would be resistant to the accidental optimizations/resizing that will be applied to the JPG?

It's a polyglot file. JPEG decoders will ignore data that comes after the end-of-data marker, while zip decoders ignore data that comes before the first archive entry.

Essentially, they ran `cat pic.jpg arch.zip > output.jpg`.

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