Ask HN: How do PassPath possibilitate 12 quintillion combinations?

I feel gleefully ignorant again –guess I'm about to learn something.

How is it possible to have 12 quintillion combinations with 4 strokes? Like in this example http://www.simplyzesty.com/mobile/passpath-app-gives-you-12-quintillion-password-combinations

I get that the first stroke is one of 36 possible, all connections in any direction. And the following 3 strokes are then one of either 8, 5 or 3 choices. Not? How does that become quintillions?

Besides, 12*10^18 combinations or not, this lock is frightfully insecure in the real world. Take one look at the video and notice if you can remember the correct code. In fact one month ago, someone in my vicinity unlocked their phone this way.

I still remember that code too.