Sajan's timing of 1:58.45 is well within the OST time of 2:01.03 but quite behind OQT of 1:57.50. Aryan's time of 15:59.47 is way outside of OST time of 15:28.02.
Basically, all swimmers who achieve OQT (A standard) are guaranteed to be part of Olympics. If after inviting OQT swimmers, relay swimmers and Universality places, there are any additional quotas left, FINA starts inviting OST swimmers. So, in order to qualify through OST, one needs luck and needs to be close to OQT timing to be quite high up in the ranking list.
Apart from Sajan, Kushagra Rawat and Advait Page have also achieved OST in 800m freestyle.