All the photos I’ve seen are too blurry to tell, but maybe its just a standard mount to the side of the receiver? The dust cover is too loose to hold a zero so no one mounts scopes directly to that (there do exist rail systems that secure the dust cover more consistently, but I still don’t trust them), and while I’ve seen rail attachments for the rear sight mounting location, its a lot more rare.
Given that they have the supply chain compromised, they could do just about anything, including just putting a microcontroller in the pager circuit that sends a current to the explosive when it receives a specific signal. I don’t know if setting plastic explosive on fire will set it off, but it could be a different formulation than the regular RDX based stuff.