Those who deployed Argon2 must have deployed the reference implementation, therefore the code became the de facto standard. Khovratovich confirmed in https://gi

Those who deployed Argon2 must have deployed the reference implementation, therefore the code became the de facto standard. Khovratovich confirmed in https://github.com/P-H-C/phc-winner-argon2/issues/183#issuecomment-270814216 https://github.com/P-H-C/phc-winner-argon2/issues/183#issuec... that the code is the de facto standard and the spec will be edited to reflect this. libsodium implemented the same behavior simply because it reused the Argon2 reference implementation.