Guessing Twitter doesn't scale/thumbnail/compress already tiny images... which is probably an oversight in this case because the file size is disproportionately large.
Yeah, I guess it's possible that it's only checking dimensions instead of actual filesize.
No, the rars are in the image metadata, not in the actual pixels at all.
They still contribute to filesize.
They don't address the metadata in compression, which is probably what the bug report [1] was about. This thumbnail is over 2MB. With the metadata removed, it's only about 2KB.