Pagers, even with a cheap LiPo battery that fails, do not explode. Somebody built hundreds, maybe thousands, of intentionally booby-trapped pagers and then managed to distribute them to a large group of targeted individuals.
This absolutely screams "state actor" but all of the states that would be capable of pulling it off have disavowed any connection, as would be expected.
Posting is on-topic for s.e.d because these things had to be *designed*. Targets can be expected to cross security boundaries so these pagers had to look like normal pagers under X-ray, and had to not "smell" like explosives. Putting aside, for sake of discussion, the horror of the device itself and the evil necessary to conceive and deploy it, one has to on some level, admire the skill required to manage it.