Hmm, I don't know how funny it is, either. An unexpected "pair of colons" is just that, whether in English, Danish, Russian, Hebrew, whatever ....
Probably either a little Easter Egg, in which case it's supposed to be funny, or else a genuine mistake (Zeev's from Israel, isn't he? Heck, isn't the whole company there?)
Or, in line with the first guess, maybe they just wanted to keep PHP in the somewhat obfuscated UNIX tradition regarding naming conventions. Or maybe he/they just wanted to see what would happen ....