There's another meaning for "muggles"

"Muggles" is the title of a recording by Louis Armstrong and His Orchestra, recorded in Chicago on December 7, 1928.

The title refers to the use of the word "muggles" as a slang term for marijuana amongst jazz musicians of the 1920s and 1930s. Armstrong was an enthusiastic user of marijuana, which was legal in most American states at the time.

J. K. Rowling has indicated that she was unaware of this prior use of the term:

I was looking for a word that suggested both foolishness and loveability. The word 'mug' came to mind, for somebody gullible, and then I softened it. I think 'muggle' sounds quite cuddly. I didn't know that the word 'muggle' had been used as drug slang at that point... ah well.