Good point. In the youtube one I've watched it over and over, and I think there's actually a little black bulge very briefly visible under the fuselage, as the aircraft flies past.
As Lusche pointed out, it doesn't mean anything, as it could be unrelated footage. However, if it is the same craft, it could mean a heavier weapon than 30mm. Not large enough to be 75mm, but maybe 37mm?