The pressure cooker really isn't the tell all proof that the IED was made by some "Middle Eastern Terrorist". It is mainly a vessel in which can span an explosive in a spherical type blast radius. Thus, when packed with flechettes or ball bearings, it can maximize the radius of damage. Something similar to a Claymore (as some of you gamers know) which is flat, but curved, is a directional charge, only really covering roughly a 60 degree horizontal arc, but can effect 180 degrees.
Round, spherical object can obtain a 360 degree perimeter of death. I have heard of pressure cookers utilized in IED's, but I personally have not witnessed one. I have however, been blown up by a fucking Chiquita banana box that was stuffed with 6 - 120mm mortar shells tied into a cell phone as an RCIED. I hate those boxes everything I go to the grocery store.
But on topic, the vessel in which the IED was placed had no real significance, but it maybe a flag into the right direction.