With all respect, you may not have witnessed problematic behaviour by a young toddler in a nursery setting and therefore you may well be talking through your hat.
A child who continuously runs off, climbs on tables, pulls out bins of toys and tips them out on the floor, grabs items other children are playing with, grabs other children's food or drinks, does not engage with toys or with songs or clapping games or dancing, tries to get up and run around with food or drinks (etc) to the point where nursery workers are talking to the parent about it is a child who is presenting a real problem in a classroom setting.
If it has got to that point, the staff have found that this toddler requires one staff member's attention 100% of the time to keep this one child and the environment safe (child safe from injuring himself, environment not strewn with trip hazards, chaotic, or physically/ emotionally unsafe for the rest of the room occupants). A disruptive toddler will reduce the availability of staff for the rest of the children, and that is a problem. A disruptive toddler will also cause others to react to his presence and behaviour with tension and possibly even by pushing him away, hitting, shouting. None of this is OK but it is predictable and given the nature of toddlers it is understandable. It requires intervention by the staff, who may end up spending their days refereeing, soothing toddlers whose tower of blocks was knocked repeatedly, whose food was taken, etc.
In addition, thanks to the massive amount of extra work a disruptive toddler generates, and due to the fact that disruption that leads to a comment to a parent can be continuous, staff do not have the time to list or document all the behaviours. A toddler who cruises around a room leaving havoc in his wake and is not responsive to redirection or correction leaves everyone frazzled. Staff will try everything in their box of tricks before approaching parents.
In short, it is not fair on staff to cast aspersions on them for approaching the parents with this complaint. They don't just have it in for this child.