The sanitary sewer jet-cleaning machine uses high-pressure water to clean the sanitary sewer. This high water pressure may affect your home's sanitary sewer plumbing. You may experience gurgling or bubbling water in the toilet bowl or, in rare cases, splash out of the bowl. The water that could come from this type of incident is from the bowl itself, not the sewer lines.
The common causes of air venting into homes during sanitary sewer cleaning are:
air movement from normal cleaning operations
the use of higher pressure needed when cleaning sanitary sewer lines that have a steep slope
sewer lines running close to the building
a plugged roof vent
the size and complexity of the home's wastewater ventilation system.
So, to minimize water splashing out of your toilet bowl, the best advice is to make it a habit to keep the bowl lid closed.