Is this breaking the rules? Well, technically it is. However the leveling from 1 to 70 is the most meaningless portion of the entire gameplay loop, one still has to gear up and start to level paragon. I’m not so sure it’s worth punishing those using it, the overall benefit is so miniscule, you literally save mere minutes of time.
Maybe the streamer could deserve a short suspension for showing the method of executing the exploit but that’s up to Blizzard if they even bother.