It's hard to say what they meant with the statement taken out of context. But, it sounds like the output of the unit is sufficient to shoot at f/5.6 with whatever film they are using, with the unit placed at some unknown distance from the subject.
Most electronic "studio" flash units have a maximum output, usually measured (or, mis-measured) in watt seconds. Then, they have controls that allow the output to be reduced from maximum, either continuously or in steps that relate to quarter, half or full-stop reductions. The wrinkle is that the watt seconds metric is power consumption, not power output. Thus, as light-output efficiency varies, direct comparisons between brands is a little iffy.