https://en.wikipedia.org/wiki/List_of_San_Francisco_placename_etymologies this credits Balboa Street as being named for Vasco Nunez de Balboa, and I think it would be safe to assume the park is likewise named. There are many parks, roads, islands, etc. in CA named Balboa, and I would find it unlikely that any are not named for the same.

List of San Francisco's placenames etymologies (Wikipedia) credits Balboa Street as being named for Vasco Nunez de Balboa, and I think it would be safe to assume the park is likewise named. There are many parks, roads, islands, etc. in CA named Balboa, and I would find it unlikely that any are not named for the same.