I used to work for a big company. There were divisions, subsidiaries, and things called business units. Some operated very independently and some even competed against each other to a certain extent. I'm not sure exactly how Surly fits inside of QBP but I know that there are about 9 Surly employees.

The Surly products originally started back in the mid to late 90's as pet projects of people who were into turning geared offroad bikes into single speeds. Some of these folks were currently working for QBP and others had previously worked for them. Eventually they convinced QBP to produce and sell the products.

I met one of the creators of the Crosscheck when I put an add on craigslist looking for a particular type of cyclocross handlebars. He sold me his and they now live on my winter bike.

Edit: According to this page on the QBP website, the Surly brand is one of their independent business units along with Salsa, Civia, and others.