The elongated appearance of the parasite is called a "band form," which is commonly associated with P. malariae trophozoites.
The P. falciparum band forms when blood has been left standing. Later, you will see the true band forms found in P. malariae. Confirmation of the species requires observation of more definitive stages of both species. Definitive diagnosis cannot be made simply by looking at the band forms and deciding if it is one species or another.