I'm afraid you missed the joke ;-)  While you believe spaces are
required on both sides of an em dash, there is no consensus on this
point.  For example, most (but not all) American authorities say /no/
spaces should be used.  That's the joke.  In writing a line about "only
one way to do it", I used a device (em dash) for which at least two ways
to do it (with spaces, without spaces) are commonly used, neither of
which is obvious -- and deliberately picked a third way just to rub it in.

This will never change ;-)