Not sure.
But here goes. Most people are accustomed to base 10. We have 10 numbers: 0,1,2,3,4,5,6,7,8,9. Once we reach 9, we’ve run out of numbers. So we add a digit and make a new number: 10.
Binary is base 2. The only numbers available are 0 and 1. 0, 1…then we run out. So we go to 10.
So ‘10’ in base 2 isn’t ten. It’s what we’d call “two” in base 10. So the bumper sticker is really saying “There are (two) kinds of people,” but it’s expressing two in binary.
Binary is the language of computers, all 0’s and 1’s. Or, if you will, electrical switches are either on or off.
BTW you could have any base you want. Hexadecimal is a biggie in programming I guess. The numbers are 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F…10.
Other, more advanced mathematicians will be along to explain (and correct me) if you’re interested.