Ehrenfeucht-Fraïssé games, possible mistake in example

Question

I was reading up on Ehrenfeucht-Fraïssé and came by this example at http://www.math.cornell.edu/~mec/Summer2009/Raluca/lesson3.html

Shouldn't there be a line between b4 and b2 (or b3 and b1), otherwise I don't see how the duplicator has a winning strategy in 3 rounds. Is this a mistake or ami I missing something?

thank you.