The distinction between a "planet" and an "exoplanet" can vary with context. In the scientific astronomy community, a planet is technically defined as a body orbiting the Sun, and all other planet-like bodies orbiting other stars are termed exoplanets. However, even professional astronomers will often use "planet" to refer broadly to all exoplanets and Solar System planets.
The precise definition of a planet is controversial even within the astronomical community. In Universe Sandbox, there is no distinction between the way planets, exoplanets, moons, and large Solar System objects (i.e., dwarf planets) are simulated, so this type of categorization is less important.
The physical properties of the Solar System planets in the Universe Sandbox database, including their mass and radius, as well as their orbital elements, are sourced from NASA Jet Propulsion Laboratory's Solar System Dynamics website.