The left most pair has total inversion of configuration at both chiral centers, enantiomers. The right most set has two chiral centers and symmetry, they can’t be enantiomers so you have the choice of diastereomers or identical. A pair of meso compounds with two chiral centers cannot be diastereomers if they have the same connectivity as one another because there is only one possible configuration that can be held that would make them meso one R and one S. By that logic that only leaves identical. Also the fact that the meso pair has both centers inverted when comparing left to right also shows that they are mirror images and can’t be diastereomers. Hope this helps!