Helio longitude (HLng) is the ecliptic longitude as seen from the Sun. The calculation of the position of solar system bodies always begin with the heliocentric ecliptic coordinates (longitude and latitude) because these object orbit the Sun. The heliocentric coordinates then get converted to other coordinate systems.
Geo longitude (Lng) is the ecliptic longitude as seen from the Earth (Geo), but otherwise, the coordinate system is the same. Based on the heliocentric coordinates of Mars and Earth, the geocentric longitude can be calculated. Naturally, the parallax of observing from the Earth causes the values to be different.