On second read the introduction of a C1-C2 alkyl is not the big deal here but rather the omission of C1 in the C2-12 language.

That whether or not this was an obvious error should reside with the court or a jury may be a reasonable point to appeal, but the legaleze arguing that it is a matter for the court and not a jury by the judge is above my head. As a lay person reading this it seems enta patent lawyers were sloppy and most likely they meant to include C1-12 given language the expert points out referring to 1-12 substitutions