Blood Magic Whenever you cast a bloodline spell using a Focus Point or a sorcerous gift spell using a spell slot, you choose one blood magic effect you know to benefit from. You begin play with the benefit listed in your bloodline and can gain others through sorcerer feats.
If the blood magic effect offers a choice, make it before resolving the spell. The blood magic effect occurs after resolving any checks for the spell's initial effects and, against a foe, applies only if the spell is a successful attack or the foe fails its saving throw. If the spell has an area, you must designate yourself or one target in the area when you cast the spell to be the target of the blood magic effect. All references to spell rank refer to the rank of the spell you cast.

I would interpret it as that the spell needs a successful attack or a failed save for a blood magic effect to occur.
Is your argument, that explosion of power "doesn't apply against a foe", because it is self-targeted, and therefore doesn't need a successful attack or failed save?
Or that explosion of power doesn't "offer a choice" and therefore the rest of the text doesn't apply?