I don't think anything after the second jet's merge was deliberate. NASA's HARV is the only F/A-18 with a thrust vectoring exhaust designed for it, and it's doubtful that similar kit would go on an EW jet.
What's shown in the video appears to be some form of slipstreaming by the chase craft that causes them both to lose pitch authority, pulling up into a stall state and then a yaw tailslide.
Cue the development of a limpet drone that would be enough to take down one of these birds in a non-destructive way… although perhaps these ones in particular would be uniquely positioned to deal with such adversaries.