To be fair it only claimed "near self-repairing".

Exactly. You can place a patch with some glue over a hole in fabric to achieve the same thing in a traditional garment. Iron-on repair patches are also similar.

It's one thing to say "get it wet and leave it in the sun". It's another thing to require identical replacement material and nutrient slurry (I don't know about you, but I think I can source fabric glue more easily than potato water).

Does the fresh fungus need to be genetically identical? I read something about mycelial nuclei in high school and it was weird.