Original wiki usage of this phrase was in the CowboyCoding page to refer to a group of cowboys working together.
It is inappropriately disparaging to companies that had to start in a garage-like place, where the workers may not be cowboys. I do some work in a basement, and yet we don't just cowboy through everything.
Did AppleComputer count as a garage shop enterprise? Did HewlettPackard? If they were, at what point did they cross over to become "respectable"?
Is Apple respectable again? I guess the iMac did it. Thankfully.
From CowboyCoding:
See also DevelopmentTeamModels
Sony where also originally a backyard enterprise in Tokyo after World War II.