Is it true that toddler learns more, understand more, interacts more while staying with grandparents then parents? As grandparents are always around them and keeps interacting and teaching them and being more experienced. It also becomes more interesting if your grandparents are well educated especially in country like India.

Yes, in a way it is true, because they get to see things apart from their parents' perspective as well. Grandparents patience and experience teach them also many a things and kids subconsciously pick up good things from their personalities. Grandparents tell children stories and things that belong to their generations and what all used to happen when they were kids. They keep the kids attached to their roots.