It's the same word. There's no distinction between them. Writing "daemon" instead of "demon" is the same thing as writing "paedagogy" instead of "pedagogy".
There is no inference available to be drawn.
> The usual ancient Greek sense [of demon], "supernatural agent or intelligence lower than a god, ministering spirit" is attested in English from 1560s
Or as Merriam-Webster will tell you:
> demon (noun)
> variants or daemon
> (usually daemon) an attendant power or spirit: GENIUS
Maxwell used the ordinary spelling of a common word. Why would anyone assume he meant to write something strange instead of something normal?
> people who weren't experts in Greek mythology
The word isn't really relevant to Greek mythology. It's relevant to Greek philosophy.