Further information: one of the cubesat payloads separated into seven different bits (three payload spheres and four sabot pieces). Another is at least two pieces when deployed. Note that the cubesat launch system is spring-loaded, intentionally scattering the payloads.
So you'd expect at least 15-16 objects from the launch; 20 isn't all strange.
If anything exploded, it would have to be second stage after payload deployment-and that wasn't shown in broadcast.
It is vaguely possible that "fail to relight" was used to say "explode", but that is very evasive even for SpaceX. Also, explosion is not a common failure mode for liquid rockets (until they crash).
Anyway, rather unlikely. If those radar sigs are real they are probably fuel or cube sat launch bits or something.