alt Hacker NewsMy unsupported non-conspiracy opinion:
A) They notice that it would land in the middle of nowhere and decided to not destroy it. It's better keep the interceptors for one that is going to hit an important target.
B) They partially intercepted it, perhaps only broke the motor or a fin, but the explosive head was intact. So instead of going to an important target, it crashed and exploded in the middle of nowhere.
(A) is extremely plausible. It is well-known that Iron Dome specifically avoided targeting rockets for interception when they not going to land in areas with people or infrastructure.
The main reason for this is because the interceptors are very scarce and costly.