Let's consider the following example of an action that an enemy (Guardian Naga) can perform during its turn (emphasis mine):
Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: 8 (1d8 + 4) piercing damage, and the target must make a DC 15 Constitution saving throw, taking 45 (10d8) poison damage on a failed save, or half as much damage on a successful one.
It's clear to me here that if the attack misses, then the target doesn't have to make the saving throw.
But then let's consider for example the following attack (Otyugh):
Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 3) piercing damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw against disease or become poisoned until the disease is cured. [...]
In this case, if the attack misses, does the target have to make the saving throw or not?