I think the memory here applies to people they have fond memories of + the strongest they know. It would explain why Gray would think of either Lyon or Ur because he held them dear as well as acknowledges their abilities.
Double fucking standards lmfao.
It's nice to see though that he's finally understood what his feelings were towards Yamada, nice change in just 14 chapters.
Edit: Also goddamn yeah that's a lotta damage.