This would be what I'd call a "gardening experiment". If your conditions are exactly like your neighbor's, same variety of onion, same planting time, same planting coditions, then good chance you'd have the same results. Otherwise, who knows? (I have not tried this experiment before. So I'd be interested in your results.)

The onion that you plant is not the same onion you will harvest. It is like planting an onion set. The new onion will form inside the mother onion which will turn to mush. You may end up with 3 or 4 baby onions. You may also leave them in the ground over winter and harvest nice crisp green onions next spring. Planting onion plants is an altogether different thing.