Comment by rdl
Seems more likely their explosive implant used a separate RF trigger -- makes the whole thing much simpler for them, less detectable. They could run a plane or drone overhead to send the radio initiate message.
Looked like 5-10g (maybe up to 20g?) of explosive, NOT battery. I think you could fit the whole package inside an AA battery, along with an AAAA battery, so you could do something crazy there, or just replace a rechargeable battery pack with something of smaller battery capacity containing the explosive, some electronics, etc. Or just use spare volume inside the case and hope no one does gross physical inspection.
It's trivial to sniff a data line to the LCD and look for a specific message(I regrettably had to do this in the late 90's to fix a bug using an additional Z8 microcontroller). That said, it would be more work than inserting a separate module with its own message reception logic.