"At least eight people were killed and 2,750 others including Hezbollah fighters, medics and Iran's envoy to Beirut were wounded on Tuesday when the pagers they use to communicate exploded across Lebanon, security sources and the Lebanese health minister said...
Lebanese internal security forces said a number of wireless communication devices were detonated across Lebanon, especially in Beirut's southern suburbs, a Hezbollah stronghold. The pagers that detonated were the latest model brought in by Hezbollah in recent months, three security sources said."
its going to be #2, that was not a Lithum Ion explosion, the batery would have far more flames and fire
Sorry to say but not great opsec by Hezbollah. I get not opening all of them but they should have opened some at random just to check for the possibility of electronic hardware bugs. Unless it was packed into the lithium cells themselves which might be possible. Heck for all we know they found a way to mix explosive compounds into the lithium itself in a way not visible by physical inspection and only by chemical analysis and perhaps subjecting them to a higher than normal voltage or something triggers the reaction.
Edit I really am going to lean on the idea of either some sort of contaminant introduced into the lithium cells designed to make them more dangerous and likely to explode rather than just burn or some sort of explosive compound mixed in with them that required the battery be overloaded for it to go off.