Ok, so based on this article and the fact that they won’t say what the explosive was, but that he used it in the past and that the ignition source seems to be shooting it with a rifle, I am betting the explosive was several pounds of Tannerite.
If you dont know, tannerite is a compound comprised of a combination of oxidizers and a fuel, primarily aluminium powder, that is supplied as two separate components that are mixed by you. It is a fairly safe compound and won’t ignite/explode unless it is hit by a transonic round. Even small arms fire from pistols and actual fire won’t set it off. It is typically used for an extra bit of fun while target shooting on private property. But if you mix together large enough batches, you can really cause some damage.
There was a youtuber called FPSRussia and he used a large batch on an old car and the resulting explosion sent a large chunk of shrapnel at him with enough speed and power to kill him if it had made contact.