It might be a reference to that 1977 paper in name, but unlike that Backus paper using math to make its point, this reads like a shallow ad for using the Curry language. The central (and only) point is merely an
example of rewriting a Prolog predicate for appending lists into Curry but without even the claim of generality. The rewritten Curry functions however trivially fix determinacy and variables to input and output roles when the entire point of logic variables in Prolog is that they're working either when bound to a value upon entering a predicate call, or can get bound to as many values indeterministically as needed until the procedure terminates succesfully (and then even more on backtracking over failed subsequent goals). The paper also glosses over the concept of unification here. I sure hope the referenced detail papers come with more substance.
The paper title doesn't even make sense? So he wants to "liberate" Logic Programming from predicates? Predicate Logic is First-Order Logic ... ie what YeGoblynQueenne says in another comment.
From a mere practical PoV, who is the author even addressing? Prolog, from the get go, was introduced with NLP, planning problems, and similar large combinatorical search spaces in mind and is used for the convenience it brings to these applications. That FP could theoretically be more broadly used is completely besides the point; Prolog's focus is its strength.