Used to know someone who worked for a mass production company, outsourcing big clothing orders for UK supermarkets.

It's common for clothing producers (Designers were in the UK in this case, clothes made in china or otherwise) to just pick whoever is in the design office that's about the right size and use them as the basis of all sizing measurements for a given size.

I've even heard of a petite woman being used as the size model for boys 11-12 age supermarket clothes. There's very little thought involved, it's just convenience to be able to tailor the template garment to a real person who's nearby.