First, you're making a pretty big leap to assume he had an irrevocable trust. Even if he did, you're making an even bigger leap to assume he funded the trust. It's amazing how many people do their estate planning, create a trust and think that's all there is to it. If the trust wasn't funded, or if the proper mechanisms weren 't executed properly to fund the trust upon death it's effectively meaningless.
Basically what that means is all real property would need to be titled to the trust outright or the will must instruct transfer of the deeds to the trust upon death. If bank accounts and other investment accounts were not titled in the ownership of the trust the transfer would have to take place via the will. All personal property or proceeds from such would need to be transferred to the trust via the will. The estate cannot pass along proceeds from anything, or title or deed to anything until debts of the estate are paid. Even if he tied up real property(real estate) and bank accounts or investment accounts in an irrevocable trust they may be accessible to pay claims depending on the terms of the trust. Many people create trusts as part of their estate planning, naming themselves and their spouse as the initial beneficiaries of the trust. If this person had an irrevocable trust and had placed his real property holdings and a portion of his financial instruments in the trust, designating that they are for his benefit during his lifetime and then pass to whomever he designates upon his death as subsequent beneficiaries, they are not automatically now earmarked for those beneficiaries until the debts of the estate (his debts) are paid.
The suggestion that assets of an irrevocable trust are guaranteed untouchable is pretty remote. At the end of the day, there's no way this person had enough assets to pay out the claims certain to be coming.