When it comes to alternatives to traditional plastics, “plant-based” or “bio-based” usually means just less petroleum, not zero petroleum.
Many “plant-based” and “bio-based” plastic alternatives contain a portion – and sometimes a majority – of petroleum-based (i.e. traditional plastic) components to make them work.
If you’re looking for petroleum-free (traditional-plastic-free), you need to find a “plant-based” or “bio-based” plastic alternative that specifies “100% traditional-plastic-free” or “100% free from petroleum-based components” or the like.