Did the balloon have enough heat to trigger the seeker or did the pilot have to aim the missile and it exploded when it got close?
https://twitter.com/MergeNewsletter/status/16219846548981104...
Boresight shot towards a slow, non-maneuvering target plus laser fuze should be just fine.
There is no publicly known way to fire an AIM-9X without seeking. It can be fired with out the seeker having a lock and given updated guidance from the launch platform via datalink to direct it towards the target so that it can then acquire the target with its own seeker. Even in BORE mode, the seeker attempts to acquire the target immediately.
The fuze is a set of two separate mechanisms, an active IR laser and photodiodes for the non-contact fuze and a contact fuze.