Spain's Ministry of Health lists conflicting information regarding arrivals. Buried deep in all the text it says that travelers arriving by sea, even from a non-EU country do not need to complete a SPH. As others have mentioned, the current form only provides the option to arrive by air.
Passengers from 12 years of age, who arrive in Spain by SEA from countries that DO NOT belong to the European Union or are NOT considered Schengen associated countries must be in possession of one of the required health certificates (vaccination, recovery or diagnostic test), whether it is an EU CCD/EU Equivalent or another type, without being required to complete a health control form.
https://www.sanidad.gob.es/en/profesionales/saludPublica/ccayes/alertasActual/nCov/spth.htm
To obtain a definitive answer, I called the Ministry of Health yesterday - they have customer service agents who can assist in English and she confirmed that cruise passengers no longer need to fill in the health form. I suggested they update the website when possible, and she said "they were working on it".