Of course children copy each other and learn together, but playing the blame game doesn't help anything. I completely agree with all the previous posters, that you should let the parent know that they should correct inappropriate behaviour at home just as you do at daycare and keep teaching the child what is and is not acceptable.

Just wait until this child starts school with 25 other rambunctious children. Remind this parent that at least their child is in a small group now and this is the tip of the iceberg of things to come.