I think that "street cred" was used ironically in this instance, because the point of the article was that any appeal provided by the old GJ was based more on a sense of spectacle than anything else. No one cared, no one was particularly entertained, and using a nonsense term to refer to the Queen's connection to the people only reveals how out of touch she truly is.
if you have street cred, it means you don't have street cred.