The article is correct only in the sense that that is the purpose of many manufactured microplastics, and the teenager's quote hints at it: "The method used was most effective on fibres obtained from a washing machine and least effective on polypropylene plastics".

I strongly think it's the majority, though I don't have a source, that most microplastics come from wear and other sources. From consumer sources, microplastics come from synthetic fibers and wear from regular plastic products, among others.