No, Saudi Arabia has not announced plans for a women-only city.
The Guardian article only says that all the workers in the cities will be women. Not all the residents. And that's based on a misreading of the original press-release, which makes it clear that there will be opportunities for female and male entrepreneurs, female and male employees, and female and male residents.
The original press release from MODON, the Saudi Industrial Property Authority, that the news outlets based their articles on, says (my emphasis):
MODON begins Planning and Development for the First Industrial City being readied for Women in the Kingdom
Al-Ahsa 2nd Industrial City will create job opportunities for both men and women
MODON has initiated works for planning and development of the first industrial city being readied for women workers in the Kingdom. It will be launched in Al-Ahsa 2nd Industrial city which is located in Hofuf near Al-Ahsa airport.
According to preliminary studies, the area allocated for Al-Ahsa 2nd will accommodate approximately 50 industrial projects. MODON will provide land at discounted rates to businessmen and businesswomen to establish their industrial or service projects. They will have the option to choose the type of industry on specific terms of preservation of the environment and safety of workers. Special sections and production halls will be reserved for women within the factory, i. e, the city is not closed or not intended for women only.