Even something like Mandelbrot or Julia sets (or similar fractals) are fully deterministic algorithms, but the choice of the position and scale (quite a small initial input) is sufficient to generate a large variety of interesting results => procedural generation.

The procedure must be making some kind of sequence of choices that leads to a set of diverging final outcomes. The choices can be prescribed by some kind of input value, or determined by a PRNG of the generation procedure itself (also actually a deterministic sequence).

However, not everything made by a computed program should be called "procedurally generated". Word docs are not a result of procedural generation. Arithmetic operators and sorting algorithms are not procedural generation techniques by themselves (although they can be used in procedural generation as building blocks).