Presumably it was Toyota who sent you the recall notice? That would seem to leave them on weak ground why they choose not to accept some responsibility, especially as the reason they have mentioned is age rather than the cause of the failure.

From a third party viewpoint I'm not sure whether the description does match your 'explosion' - it states in extreme circumstances if ejected oil gets into contact with an ignition source, it may cause fire.

Have you asked Toyota what their next step is? Will they be sending out one of their own technical people to evaluate the damage to your engine?

By the way the recall system isn't a warranty. If a car has been affected by the problem(s) the recall is meant to address, then the recall will correct the problem and subsequent damage. However, if the reason for the engine damage is something outside of that particular recall's remit, then the recall won't cover the damage.

If Toyota state that the engine damage is due to something outside the remit of this particular recall, you will be reliant on either an extended warranty (if you have one), or a goodwill contribution from Toyota.

You stand more chance of receiving goodwill if you have a Toyota service history. If you haven't got a Toyota service history, Toyota (like any other manufacturer) may not offer any goodwill.

Goodwill works both ways - if you're loyal to the manufacturer in terms of where you get your vehicle serviced, then the manufacturer will usually show some loyalty to you in terms of goodwill.