+Alaina Boswell , the joke is that the meme has incomplete data. The rest of the saying would say "and those that cant". By extrapolating from whats given you can determine that "and those that cant" is the rest of the joke.
I wasn't even paying attention to the cat at first I was looking in the background and saw the 2 rats, 2 pieces of cheese, and a bottle of milk, and I thought: What the hell was Einstein thinkin'? then when I looked in the foreground I was like: Oh shit it's a cat!
Couldn't the people who don't believe there are two types of people instead believe there are three (four, five, ...) types of people and bring the whole idea of types of people crashing down due to stack overflow?
Funny, but one might argue that perhaps there are two other groups, those who CAN'T extrapolate, and those who refuse to extrapolate from incomplete data lest they make fools of themselves (maybe by saying something like, "hey these neutrinos move faster than light") and wait for the complete set to be gathered.
The point was, he gave us one variable with two possibilities (person.canExtrapolate). He then defined one on the variable's possibilities. That one defined one implies that the variable is a boolean (people.canExtrapolate(true) or false). Also, extrapolate basically means "extending something to an unknown by assuming." If you couldn't grasp the concept then you really shouldn't be on the internet (if all of you were being sarcastic, sorry for not getting it).