I think it really isn't something that's going to instantly transform the skills, imho it really takes a fair bit of work go fully get accustomed to the particular camera and lens combination (even a battery grip may significantly affect it) they need to be held exactly at the right balancing points (it may even depends on the hands of the person, with the RF 50 1.2 one could use the left pointing finger to extend underneath the lens and reach all the way to the front to keep it more steady) I think seeing the center point in the viewfinder may give a hint about how steady it is with the help of IBIS.
And the shutter has to be tipped lightly but decisively at the same time (that's not easy...the 2 sec timer does not work unfortunately, as by the time it takes the picture, you will be more shaky).
The position of the Canon shutter may make it a bit tricky, because while it sits at a comfortable place, it is pressed down at an angle, so it can cause a slight movement on multiple axes.
There may also be a difference between mechanical and electronic shutter etc. so plenty of variables. My best results (that do reach the quotes 5 stops lens IS of the RF 24-105mm lens) are not really repeatable and I really need to concentrate.
Looking at the examples from article like this one and some of my own attempts, it seems that sometimes the camera manages to keep the center sharp, but towards the edges, the stabilisation effect may not succeed. I guess with a good enough technique and multiple attempts, it is possible to makes this one sharp through the whole frame.
And of course looking at it like this you can see that the article is clickbait, it is not going to be that good as claimed in the title...