The hunters were located 350 yards (not 200, as had been stated in the report -- see the map with legend at the link) and 400 feet downhill from the firefighters.
Any city dweller who's lived near a freeway, or experienced backcountry hiker or hunter, knows that sound travels uphill far more readily than it travels downhill. It is also affected by the pitch and the wind. Again, I live here. I can't say for sure about August 23rd, but August was a windy month here. And the area where this happened commonly has strong east winds at this time of year.
It is very easy to logically speculate that it was easy for the firefighters to hear the gunshots, but impossible for the hunters to hear the firefighters shouting from 350 yards away. I have a 300-yard firing range on my property. I can easily hear gunshots, but I couldn't hear shouting at that distance even on a calm day.
Finally, hunters wear ear protection, either ear muffs (which is what I do) or ear plugs, and sometimes both. That would have sealed the deal. But wait! You're Eurotrash. You made your conclusion on the basis of a report that you did not carefully read, and without reading the other reports from local sources.
Carry on, then. You know nothing, but you'll tell us everything. It's what you Londoners just love to do.