Not necessarily true, siswa is generally for males and sometimes to refer to general groups of students whereas siswi is exclusively for females. pelajar is gender neutral.
You will see signs that say "Menerima mahasiswa/i" Accepting Students.
We're actually trying to make words genderless, by using less words like mahasiswi, karyawati, wartawati. Although these feminine nouns are still used, words like mahasiswa, karyawan, and wartawan apply to women too.