The parent commentor is not using any domain-specific jargon. They just mean the normal meaning of the abstract adjective "plastic": capable of being permanently deformed/bent/altered in a way that does not then return to baseline (contrast elastic). Conceptually derived from "plastic deformation" in physics: when you bend something enough that it doesn't bend back any more.

Usages of this sense of "plastic" appear all across the English language: brain plasticity; plastic surgery; a cancerous neoplasm.