It's even mentioned in that article how to get around the fix they put in so you couldn't target a group of less than 20 people.
I'm not sure if this particular method still works, but let's take a step back and think before we make claims about what is and is not possible in a complex system with lots features and knobs to twiddle. Whether this was an emergent feature from other features of the system or a specifically desired and designed behavior, at least at one point Facebook allowed very fine grained targeting.
1: http://ghostinfluence.com/the-ultimate-retaliation-pranking-...