That ID gap is aligned with the 32-bit integer limit, which was manually breached as part of the 1st Tweetpocalypse (http://bit.ly/28MVIF3). It would seem likely to be internally created accounts that re-used that ID space later on.

everything old is new again

Full width characters are used to maintain alignment in east Asian languages. A good example is the Chinese encodings, where every character is more or less square. If you put a half-width (e.g. latin) question mark in there is would throw off the natural alignment. A full-width question mark however keeps the alignment by taking up a full square. Might seem like a silly distinction but Chinese typesetting (even web typesetting) expects squares, and so do the viewer's eyes.