With a bunch of cameramen & reporters nearby in a open-air election campaign settings, in a country where private gun ownership is near non-existent, would you immediately suspect something to be a improvised gun?

The cartridges being homebrew with slug shots, the first shot was described more as electric substation going off, some malfunctioning sound equipment etc - not the shotgun type gun report. The second shot around 1.5-2 seconds later had sufficient smoke discharge to be identified as firearm (Information quoted in Wikipedia). The sounds caught on video clip is significantly different for loud sources (e.g. try comparing aircraft engine sound on YT with your recollection of live sound). Hence its harder to know how it sounded like & assess for yourself