Not a joke, whether in, funny or otherwise.

Free could mean either of two things:
If I talk about "free beer", I mean I don't want to pay for it.
If I talk about "free speech", I mean I don't want restrictions on it.

From RMS's paper here:

Free software is a matter of liberty, not price. To understand the concept, you should think of free as in free speech, not as in free beer.

As time went on, "free as in free speech" became habitually truncated to "free as in speech", and "free ... as in free beer" to "free as in beer", because everyone talking about it knew precisely the distinction being made, and it would be horrible to waste a monosyllable everytime you refer to one or the other. (I suppose, if you wished to find humor in this, that would be the place to find it; with our silly obsession for conciseness.)

Further truncations like "beer-free" and "speech-free" are occasionally heard, but that sounds too much like non-alcoholic and uncommented code to gain much currency.