If you see studio strobes on softboxes and umbrellas there, the reason is simple. These strobes have built-in slave units. They will fire in unison with any flash of light.
The photographer would probably want the studio strobes to be the subject's main light source, along with all the key light, fill light, hair light, background light, and backlight.
By tilting the flash head AWAY from the subject, it is not as affected by the camera's flash, but will still trigger the studio strobes.
Some people also use an IR flash trigger to do the same thing.
Regards
CK