Britannica says the bomb maker was inspired by Inspire, an Al-Queda linked website.
They don't say what the explosive was that was used in the bombs. However the article (OP) says that "bomb making materials" had been recovered, including acetone.
Acetone is used in making TATP, a popular, but tricky explosive that is favored by jihadis, and known among them as "The Mother of Satan", for its characteristics. It is also chemically unstable and perishable, that is, it degrades in efficacy with time and exposure to air. It is a primary explosive, sensitive to shock and friction, especially if dry.
(Yes, I read a lot of "comic books').
So, while the presence of acetone would fit the profile of a jihadi bomber, there are other uses for most anything that can be adapted to use in an IED, or even to make the explosive I suspect was used. If anyone has any actual knowledge ora source citing the explosive, that might determine if the presence of acetone was relevant, or possibly incidental.