My point is that two opposing factions had numerous examples of the same basing feature.
This could be Goblins looting an Idoneth treasure trove, or Flesh Eater Courts, or Seraphon, or yes, Idoneth Endless spells. Or it could be Noise Marines on an Aeldari Craftworld. Unless you work for GW, all of these are equally plausible but none of them are certain.