Frankly, doesn't even sound like much. If we assumed 1kg per clothing article made of plastic, that amounts to 37,000 tons per year. Even in Sub-Saharan Africa, it is estimated that waste produced is approximately 1kg per person per day for a total of 60 MILLION tons per year.

It isn't good to send unusable trash to Africa but this hardly scratches the surface percentage wise and that assumes that non of these plastic articles of clothing are usable which is rather unlikely.

Of course the other odd thing is that clothes with some polyester, rayon etc are normal so labelling them as "plastic" is kind of misleading at best. (it is likely that any clothes with elastic band will contain some form of rubberized plastic materials, for example)