Two points:
AIM-120. If one were to sit with a child and draw a missile that was designed to go towards a target (can’t think of any that aren’t) you probably have an order of march something like: Seeker, guidance unit, some fusing device, frag and ‘energetics’ - then all the petrol and anything else you’ve forgotten. Given the position of the target you’d probably find a clever way of getting it to explode outwards (bit of a given) and preferably forwards. Ergo no real surprise if stuff behind the warhead survives in some form or another.
Ref the Mig-21 being there. Could be as simple as using the simpler aircraft to detonate the air picture for the big boys to tidy up. So long as the detonator escapes and the big boys tidy - not a bad idea. If the detonator ‘collects one’ then you’ve ‘sort of blown it’. Obvs I’ve got no idea what he was doing, hope his back’s OK. Never been a Mig-21 fan myself but it does have supporters - and the Romanians in particular fielded quite a cheeky variant.