Theoretically, pagers are simpler devices, meaning it would be much easier in principle to analyse both hardware and software to check for issues, unlike a mainstream phone OS which has a bigger software attack area and can have at least some zero day attacks known to a state level actor like Israel.
Although, if it really was explosive inside the pagers it seems Hezbollah didn't do this.
That does sound like spy novel stuff but it seems plausible enough? Dude was turned, and he wanted money and an escape to somewhere safe in exchange for cooperation.
So, it will really matter when everything runs in a container or AppArmor or something like that. I wonder if that will ever be made convenient and "it just works" without having the impression of having apps being on somewhat inconvenient silos.