Bioplastic can be 100% fossil based. Bioplastic can be 0% biodegradable. Are you confused?
Below picture will help you to navigate in the universe of biobased and petrochemical based plastics including their degradabilities.
For instance, polycaprolactone and poly(butylene succinate) are delivered from petroleum, but they can be degraded by microorganisms.
Despite the fact that polyethylene and nylon can be produced from biomass or renewable resources, they are non-biodegradable.