That technique has been preached for a long time, Mark Chisholm popularized it afaik.
In a woods setting where stumps are clean its ok but I would never use it in a residential setting where stumps are likely dirtier, cutting with a pushing chain causes rapid dullness. Using a wedge, or twigs, or Tucker's technique of cut a tiny wedge are all better imo.
I also think pushing all that sawdust into the kerf will result in slower cutting/chain speed compared to pulling it all out into mid air where there is far less resistance, but that is just a supposition.