I rushed and misread the prepositional phrase one, too (rushed clicking on the answer, I mean) so also got 13/14.
80s comp - no grammar lessons at all - but did do French and German A Level and so knew lots of grammar from that - including gerund. Also knew lots of rhetorical terms etc from English A Level. Can't believe so many don't know 'gerund' who did do languages?
I did a module on grammar, including parsing, as part of English Lit degree and the range of grammar ability we'd all come in with was astonishing.
I also agree that being able to use grammar is more important than knowing the technical terms - though, to some extent, you can't have one without the other. Listening to year 7s the other week going over the difference between subject and object (so, for example, they knew when to use 'I' instead of 'me') reminded me that both are important.