Far as I can tell, "pattern-matching facilitates indexing of rules" means that the indexing scheme builds an index with a key for every instantiation pattern of a predicate in the program database.

Prolog uses pattern matching to match a query (or a goal) to the head of a predicate in its database. To speed things up, predicates are indexed by their functor name (the predicate symbol) and the value of their first argument, if it is a constant. That's all for default Prolog.

In modern Prologs keys are built for deeper patterns- more arguments, or compound arguments at different depth etc. The particulars depend on the implementation, but basically what I get from "pattern matching facilitates etc" is that Picat allows indexing on multiple arguments, including compound terms, which could enable matching the entire pattern of a query to an index key. Which is cool and all but it's not something you won't find in Prolog.

You can find details of one indexing scheme for Prolog in Swi-Prolog's documentation on its jiti clause indexing, here:

http://www.swi-prolog.org/pldoc/man?section=jitindex

Hope the above makes sense- I assume some knowledge of Prolog, let me know otherwise and I'm happy to clarify.