Well not exactly. Although, Giratina is based on GRAVITY. There are more than 3 creation Pokemon... I mean 3 states of matter anyway, you're forgetting Arceus. But Dialga and Palkia are based on time and space respectively. Dialga is steel type because time is still-moving and constant, never getting faster or slower like a solid. While Palkia is water type because of the vastness of space is similar to the vastness of the ocean. And Giratina is ghost type because like gravity, ghosts are all around us but we can never see them with the naked eye, ghosts are also the most gaseous of every type (I.E gastly). Arceus is plasma because of how many different things plasma makes up, (99% of our known universe) this is like how Arceus is every type, and also omnipotent because its literally everything. They all fit their respective themes while also having the states of matter, because Pokemon can in fact have more than one inspiration.
Tl:DR Creation Quartet can have more than one inspiration and are based on matter.