The guitarists are simply playing inversions of the same chord. For instance, player 1 plays A, D & G open shapes (no capo or barre).
Player 2 can play inversions of those chords using a finger barre or a capo on the 5th fret and play E, G & D shapes.
Same chords, different positions. If player 1 has downtuned to Eb, player 2 can either also downtune, or place the capo 1 fret lower to achieve the same effect.
Check out the CAGED system for more info.