Most plumbers wont mess with the septic tank. We deal mostly with components inside the house. Did you have a vent pipe in the yard (often looks like a candy cane made of PVC) before the repair but not after? If all he did was replace the line it shouldn't cause a smell inside the house. All plumbing fixtures inside the house should have properly functioning traps. Those traps would create and maintain a water seal against the sewer gases. You should have at least one vent through the roof to equalize pressures within the drainage system. This prevents positive pressures within the system (caused by fixtures discharging into the lines, ie toilet flush) from pushing gas out through the traps, and negative pressures (the waste in line will pull air behind it like your finger over the end of a straw) from sucking water out of the traps.
The word "plumber" dates from the Roman Empire. The Latin for lead is plumbum. Roman roofs used lead in conduits and drain pipes and some were also covered with lead, lead was also used for piping and for making baths. In medieval times anyone who worked with lead was referred to as a plumber as can be seen from an extract of workmen fixing a roof in Westminster Palace and were referred to as plumbers "To Gilbert de Westminster, plumber, working about the roof of the pantry of the little hall, covering it with lead, and about various defects in the roof of the little hall". Thus a person with expertise in working with lead was first known as a Plumbarius which was later shortened to plumber.