It's an expression - similar are 'Joe Public' 'Joe Soap' and so on, used to indicate a typical man-in-the-street figure, just any anonymous individual who can represent the population in general. It's probably evolved because Joe is a simple common single-syllible name, and 'Blow' is a simple rhyming word, esy to remember, easy to slip into common usage.
Regarding the "Where did it originate?" part of your question, the answer is that 'Joe' was used as far back as the 1840s in the USA to mean just any chap - or 'guy', as Americans themselves might say. The first time 'Joe Blow' appeared in print was a century later in a dictionary of American military slang. Joe Bloggs and Joe Do(a)kes were alternative versions.