Reading a bit more into it, seems all of them were Motorola Apollo Gold pagers (I stand corrected), so they had to have exploited the li-on charging pins to either create a loop causing thermal runaway, or spam different voltage discharging signals via their payload. Regardless, it's a truly impressive exploit.
The newer gapollo ALA25v6 by Apollo is in Farsi and I am having trouble translating from pdf, but I found an older one for the ala25v4 in English here: