What are the chances someone not knowing SQL, and need to do something with SQL actually picks up a book...

We were talking about non-trivial!! Even intelligent programmers usually don't start with complicated joins when they do their first projects with a database (when they have a choice). My first steps with SQL were pretty basic and could easily have been done within the confines of Class::DBI

Have you actually used Class::DBI? It doesn't map databases to objects. It maps table rows to objects.

No. And I would be hard pressed to find reasons to use it today when much better alternatives are available

abstraction of database implementation

But that isn't true.

What the author meant was abstraction of the db engine, i.e. it doesn't matter if it was mysql or postgreSQL underneath. Ok, I doubt there are many differences at that level to abstract away, but it is definitely a form of abstraction