Same process, different breakdown speeds.
Biodegradable products are capable of being decomposed by bacteria, fungi or algae and will eventually disappear into the environment and leave no harmful chemicals behind. The amount of time is not really defined, but it’s not thousands of years (which is the lifespan of various plastics).
Products that are capable of decaying into nutrient-rich, natural material under controlled conditions in a commercial composting facility. This is achieved through controlled exposure to microorganisms, humidity and temperature. It will not create harmful micro-plastics when they get broken down and have a very specific and certified time-limit: they break down in under 12 weeks in composting conditions, and is therefore suitable for industrial composting.