So how do they trigger 10 bulbs with 6 contacts ?
The double contact #6 indicates the presence of a flashbar to the camera and serves as the common contact for the flash bulbs.
Each pair of neighboring bulbs shares a contact ( #1 - #5 ).
The first bulb of each pair is connected directly to the common contact.
The second bulb of each pair is connected to the common contact through a "switch". (SW1-SW5).
That switch is a patch of a substance behind each odd numbered flashbulb that is an insulator "open" at first but becomes conductive "closed" when heated by the firing flash bulb.
It connects the second bulb of the pair to the common contact so it can be detected by the camera and fired.
After that bulb is spent the contact remains open and the camera selects the next good bulb.
The same method is used to fire 5 cascading bulbs in Flipflash / Topflash Flashbars
There each burning bulb opens the contact path for the next one.
For informaton about ordinary SX-70 flashbars look here.