no, somebody gave you wrong information... the video may have been referring to an 'off grid' cabin or house that has 'grid electricity' for back up, but they try to use their solar power primarily... but that won't work for motorhomes, unless you have a HYBRID type inverter system that can use all incoming solar power to offset any needs for the grid-electric from the rv park.
now, could you simply 'unplug' from Shore power during the day, use only items from your inverter(no air conditioning, elec water heater, etc), allow the incoming solar to 'recharge' your batteries, and then only use 'grid-electricity' during the overnight for any battery charging needed? Sure. It's doubtful, though, that this method would greatly reduce your electricity charges since you may find yourself plugging back into the grid for the items that don't run on the inverter, or if the sun is not 'out'(cloudy, rain, etc).
You can always give it a try, though when there is a lot of good sun, there's usually also a lot of high heat that goes with it. If you can bear the heat, it might be worth a shot. In the long run, it's doubtful that the overall difference will be worth the effort. But, you would have to either 'unplug' or 'trip' the shore power breaker.