Yeah, this should remove any doubt that there were explosives involved. At the 500 to 1000 mA hour capacity typically used in pagers, even tampering with the battery's venting in an attempt to build up gas pressure would at worst result in a pop and some smoke from the top of the bag.

Blowing a hole in the side of the bag and sending debris for several meters is obviously not plausible with that quantity of lithium.

The explosion in the video does show visible smoke, but there is not a visible flame or fire.