see their comments on WITHIN GROUP and redundant declaration of identifiers. As for boiler plate, SQL's turf war over plain English words as reserved names creates this interesting situation of boiler plate identifiers in SQL to disambiguate from reserved keywords.
This is nothing more than one guy's opinion dressed up to look like an academic study. He actually admits a few times that SQL features are concise. SQL definitely isn't perfect, and some vendors' implementations are better than others, but things like JOINs are pretty perfect. He considers specifying an INNER JOIN as syntactic sugar (over using WHERE equality), which seems backwards, as opposed to a more consistent practice of always using the JOIN keyword regardless of the type of join.