Ummm, what? Other than what Al-Qaida is writing about--making bombs from pressure cookers and finding crowds?
The past use of this exact tactic by jihadis?
Pressure-Cooker Bomb Is Qaeda Speciality » Matzav.com - The Online Voice of Torah Jewry
Boston Marathon bombs: al-Qaeda's Inspire magazine taught pressure cooker bomb-making techniques - Telegraph
WTH do you mean assumed???
Yes, the very method you can look up on the internet so it was far from automatic. However, no one was taking any claim which was very un-jihadist. However, feel free to pat yourself on the back for being smarter than anyone on the scene...and from Lafayette.