This means Israel had to have either factories of their own, that makes them (unlikely).
These companies are lying or unaware....
or and this is much more likely.....
They intercepted shipments and then opened units up, planted bombs in them, and then put them back on the market (with non the wiser).
They must have known were hezbollah bought their pagers from (in general) and somehow gotten their hands on these and reworked them.
Still this is insane.
Imagine your Job is to break into a warehouse, open up pagers on the spot (or replace them with pre-worked on models), rework them, and then leave them there, without anyone knowing you broke into said warehouse, and altered the contents there.
For that to work, you also must know where these sales end up, what time, its likely to member goes to buy from said place ect ect.
So there's a ton of intelligence work likely attached to something like this.
Again... insane that it worked.
The thing is, something like this only works once.
You bet your arse that now, they'll learn to open up and inspect things before just buying or carrying around.