Partridge has an entry for scatty: "(Not) very mad; crazy; lower classes'" He suggests it may have come from scatterbrained or Derbyshire dialect word scattle 'easily frightened'.

As for Vulgar versus Classical Latin, I think that the Economist author has simplified matters. Classical Latin is a conservative register and was pretty much a language that was learned in school. Vulgar Latin was spoken, colloquial Latin. Of course, it's hard to keep class out of this just as with English and its various dialects. There are examples of what spoken Latin must've been like in the Plautine plays which pre-date the Roman Emprie by nearly two centuries, Petronius' novel Satyricon, and lots of graffiti from Pompey and elsewhere. Classicists differ between Golden and Silver Ages of Classical Latin; Petronius, Pliny, and Lucan are considered Silver Age authors. Some differences between CL and VL were phonological, e.g., the diphthong -au- becoming a vowel -o-, the final -m of the accusative singular being more of a nasalization of the preceeding vowel, lexical, e.g., replacing the classical caput 'head' with testa 'pot', and even syntactic, e.g., replacing ut with the subjunctive with quia and the indicative. These are also some of the things that happened or were carried over into the Romance languages as they developed. In the end, VL was pretty much comprehensible to the upper classes in much the same way that many "sub-standard" dialects of English are understood by folks who speak a more upperclass register of "standard" English. So less baseball and cricket, than baseball and stickball.