As @ezbass says, they are probably playing the same chord (a chord is just made up of a fixed group notes), just on a different place on the neck. Each chord can be played in several different ways, using the same actual notes, but just using different position on the neck, the same as bottom string and top string are both the note of E so can be interchanged even though they sound different. This is one of the benefits of the guitar, the notes are repeated multiple times on the fretboard so a player can choose in which order he plays the notes of a particular chord, or just in a position that he favours.
It is common with 2 guitars to play different positions (inversions), usually one in the lower registers and one higher up so that the sound doesn't get too muddy.