I think you're missing the compost part. Wood will break down in a compost, yet you can build houses from it. Indoor furniture made from wood will happily serve you for decades. Same with this biodegradable plastic: It'll have a shelf life of decades or even centuries. When shredded and composted it will break down. This material is likely not a good candidate for the wheel housing on your car, but there's no reason not to use it, for example, for a car's interior.
I think you're missing the compost part. Wood will break down in a compost, yet you can build houses from it. Indoor furniture made from wood will happily serve you for decades. Same with this biodegradable plastic: It'll have a shelf life of decades or even centuries. When shredded and composted it will break down. This material is likely not a good candidate for the wheel housing on your car, but there's no reason not to use it, for example, for a car's interior.