Manufacturers' past claims (hyped by the press and public) that WPC and PVC were maintenance-free certainly helped confuse things, and intense competition has led producers to be intentionally vague about what's in their products.
Should you demand to know what's in this stuff? Well, since 2004, seven wood-plastic composite manufacturers and suppliers have faced lawsuits related to a host of problems, including fading and color changes, slippery surfaces, shrinkage, swelling, and mold. In at least two of those cases, a supplier and reseller were accused along with the manufacturer.
It takes some work, but you can learn to spot the differences between products and, hopefully, avoid future callbacks. Here's a start.