I expect that “low-grade” explosives means black powder....it’s still deadly....just go to a Civil War cemetary sometimes and see for yourself what black powder can do.
It says home made explosive. Could be black powder, or something else. Home made ammex, peroxide, nitro cellulose. RDX (mind you that’s a high explosive). There are a a lot of recipes out there.
Thank Allah for dumb terrorists. They were definitely trying to make something that would explode.