That might be a copy/paste error. You can’t send events from one blue to another blue via traveler/neutral connection, so it doesn’t make sense in my head. I’m using 3-way Aux but I’m using a blue and white series; no magic binding. Let’s see if @Eric_Inovelli can confirm.
When wiring two Blues into what is currently a 3-way, you will only use two of the three 3-wire conductors between the two switches. Black for hot and white for neutral, sending a hot and neutral to the other switch from the powered box. Those conductors go to the hot and neutral terminals on the other switch.