When using the comand /perimeterinfo, it includes all nether wart blocks as spawnable space, despite any mob can spawn on it (at least in the nether).
This happened in Minecraft 1.16.1 with Carpet Mod, Fabric, Litematica, MaLibLib and MiniHud.

because they are.

You have to provide specific mob to test properly for spawning, like
/perimeterinfo ~ ~ ~ piglin
This way a specific mob will be used to test for spawnability.