The individual explosives were probably 15 or 20 grams of material that could be disguised as part of the case, components, or battery. Plastic explosives can be molded, painted, and wired to resemble almost anything.
IDK for sure, it could be as you describe, but I doubt it because the pagers were in place for months and many of them were likely disassembled/repaired in that time.
The paradox of being an antitheist is that you have to believe that religious ideas are uniquely powerful and dangerous. Politics, history, culture, and all context are just debris drifting in the mighty river of religion.