Generative compositions differ from sequenced ones in that a sequenced composition is laid out in advance and does not change. A generative composition happens as the program runs. The philosophically inclined will wonder whether generative compositions are deterministic. In fact if run on a computer they always are, because computers are deterministic. This is not the same question as whether they are predictable. Something can be deterministic but unpredictable. The answer to this very interesting question depends on whether the algorithm is seeded by truly random numbers. Computers cannot generate truly random numbers, but it is fair to say that a generative sequence can be so complex as to be unpredictable by human perception or reason.
It may include non-computational methods, for example Ron Pellegrino's 1972 processes for "Metabiosis" was an installation with lenses sensing air flow changes using light and photoresistors. Strictly it is not algorithmic, not because it doesn't run on a computer, but because the process does not follow the definition of an algorithm . Whether or not you believe installations that harness environmental unpredictability like Pellegrino's are deterministic depends on whether you believe reality is deterministic.