ah - so categories:columns is what i was looking for. I assume that's how positional columns (as opposed to named only columns) are determined.
the template::query example comes from 2002 vintage queries in ecommerce by Bart T - I wasn't quite sure why he used it either, but it's all over the place in ecommerce.
Since db_multirow takes care of all that for me, i'll just convert the calls where necessary.
Thanks Lars - as always, your knowledge is prodigious!