Title says it all, the only reason that frigate exploded was because it was substantially damage before the explosion of the other ship that killed it.
Whether ships killed by explosions should give exp is a minor concern compared to the problem of such ships often giving capture points to the wrong side. If I kill an enemy and that in turn kills an ally, my side gains cap points for both destroyed ships, because I initiated the chain. What should obviously be the case is that each dead ship count against the faction losing it regardless of who caused the death. This also applies to the concept of ships suiciding in radiation. That side should lose cap points. In the current system such suicides deny the enemy the kill exp and deny him cap points. In a free corvette this is particularly annoying. This change would actively discourage team kills unlike the current system which actually encourages them.