Election law charge means FEC violation. Can we presume that Mueller is out of luck on that angle, as it is not under his jurisdiction as a federal crime?
I think Mueller passed the lead along because it was too much of a stretch for his team to handle personally, having no connection to a person who worked on the campaign.
If Mueller found an FEC violation by a person who worked on the campaign, his team would file the charges.
I also speculated that this is a fishing expedition instigated by Mueller, hoping the search will uncover something Mueller can fold into his report.