I think you're correct, it was too loud for a pipe bomb. At least one that I would think could be carried easily. I'm no explosives expert, and what explosives I have ever used was limited to those shot off aircraft onto targets miles away. You don't hear/feel those go off. But as you know this was a deep felt boom. It also sounded to me like a big trash dumpster being rattled at the same time. Guess that was all the loose stuff within the blast radius resonating from the shock wave.
I've set off Claymores before. Setting off 2 of them at the same time will cause a 5 ton military truck to jump and bounce 50 yards away. There's not that much plastic explosive in them. Most of the weight is from the two layers of ball bearings.
A person can easily carry enough plastic explosive to make a very impressive blast.