It can either be excitement or submission, and you can get an idea of which it is by how your dog acts right before it happens, depending on if the dog assumes submissive postures or shows submissive behavior
prior to piddling. There will likely be submissive behaviors afterward, because your dog knows that piddling in the house is a no-no, so you can't judge by that.
Most of the time, when this happens at the entrance of a person your dog knows and likes or even a stranger that presents no threat, this is just puppy-excitement and they do grow out of it. Nothing to worry about - just keep a supply of paper towels and cleaning spray, lol!
Shiva did it until she was about 7 months old. Talk about BIG piddle-puddles!