I don't feel Emily's answer fully explains the meaning.

Being smooth isn't just about making something look easy. It basically means the same as "cool", but with slightly negative undertones. The old James Bond was smooth: as witty and fearless as he was, he was also a ladies' man, and sometimes he could grate on you.

Smooth
Excessively and often artfully suave: ingratiating.
a smooth operator
http://www.merriam-webster.com/dictionary/smooth

So the brand is partly poking fun at itself here.

The other important point is that "smooth" is also a reference to the texture of the Snickers bar.

Good luck translating that into Arabic!