The guys have said it all correctly ...
The reason why you throttle on hard is to create high enough cylinder pressure to get behind the rings and force them out hard against the cylinder wall ... That wears the peaks of the honing off and gives the best possible ring seal ...
The reason why you throttle on , let the bike pick up some speed , then totally chop the throttle letting it slow itself down in gear without touching the brakes is :
When the rings are wearing in , fine metal filings are produced ... If you keep on revving the engine out ... those filings get blown down into the sump oil because the rings haven't sealed yet ... When you instantly back the throttle off , the strong vacuum sucks oil upwards past the rings ... That helps lubricate the bore , rings and piston to prevent metal welding or seizing ... but the main thing it does is pulls the fine metal filings up into the combustion chamber where they then get blown out of the exhaust pipe ... instead of sitting between the rings and causing problems or getting blown into the bottom end ...
You don't want to labour , stall or idle a new motor for very long the same reasons ... If the idle circuit is too lean , you'll heat the piston and rings up too much ... plus less oil gets splashed onto the bore or pumped up to the top end at idle ... The peaks of the cam lobes can also heat up too ... they work harden over time ...
As the rings wear in ... they get hotter than usual so they expand more ... if you idle for too long or labour or rev the motor too much , they can get hot enough to butt the ends up and scuff the bore ...
That's why it's best to do your run in for very short periods at first with intermittent cooling down in between ... as the rings and bore wear in , the friction and heat lessens and the end gaps increase slightly ... once everything is properly run in , the rings and their end gaps stabilize ...
The Chinese engine manufacturers have more than likely taken into account that a lot of owners won't do the run in procedure properly ... so they most likely set the end gaps on the wide side for safety reasons ...
Drag racers use "file back" rings so that they can set the end gaps to their own specs ... the smaller the end gap , the greater the ring seal , the greater the cylinder pressure and the greater the power produced per cylinder ... But with tight end gaps ... the bed in procedure must be done spot on ...
They also use "Zero gap" second rings (ZGS) ... Childs and Albert makes them ...
You want to wear the rings into the cylinder wall in a controlled manner without wearing them too much ... so the on /off throttling procedure should be done in short bursts first ... then the rev out gradually increased as you feel the engine loosening up ...
You'll know when the rings are beginning to seal better because the engine will start easier , idle better and you'll feel it start making more power ... plus it'll start running cooler ...
Then you can enjoy a sweet running , smooth idling engine that holds it's tune ... A properly run in engine will idle steadily all day long without stalling ... a poorly run in engine will always seem like it's out of tune ... oil contamination affects how it runs ...
