It is definitely possible(start a fire).
However, you will not see a rapid explosion in lipo batteries. These are mostly gases such as lithium fluoride (LiF), carbon dioxide (CO2), and potentially toxic gases like hydrogen fluoride (HF). Generally, when batteries are produced, they are intended to be designed to release gas to the outside.These cannot explode directly. At first, you will see a gas that glows with fire. Considering that it is in a plastic part, there will most likely be no explosion. This may be possible in devices containing metal enclosure (if the gas is sufficiently compressed). if the enclosures are not designed to withstand pressurized water like flight recorders(These usually contain gasket type adhesives to prevent leakage.) (if it is a portable device outdoors), they will allow significant amounts of gas to escape.
Most user-friendly devices protect themselves from overheating.
However, the explosion in the videos looks very violent. I think a trace amount of explosives was placed inside the devices.5-10 psi with a 3 gram explosive is more than enough to kill someone. (10-15 grams fits easily into this device.)(This can certainly fit into small enclosures.)The lethal effect will be directly proportional to the area of the body where the shrapnel hits.(groin and neck area.) For such a device carried in a pocket, when all explosions are considered, it can cause deaths of approximately 5% to 10%.
The evil thought here is the call message. As far as I can see in the video, there is a call message before the explosion and the aim here is to remove the device from the pocket. Thus, the effect percentage will increase.
They could have been placed there to be destroyed remotely if the pagers fall into enemy hands or if the device is lost. (What would happen if it fell into the hands of children in terms of ethics) (ah ı forget ,war has no ethics)
If not, all that's left is the supplier network (modified pagers )(High probability)