It's the national celebration parade ground. So every 9th October there's a big Independence day parade - hence the helicopter use.
Two or Three Popes have celebrated mass there - there is a large Catholic martyrs shrine close by in Namugongo -
wiki link
I seem to remember Bill Clinton speaking there as well - as we were told to avoid the area during his visit.
The history of Uganda in the 19th century is fascinating - a couple of good books if anyone is interested (nothing aviation related, but good reads nevertheless)
by Alan Moorhead
by Charles Miler
I spent a large part of my time in Uganda about 1/2 mile away at the National Sports Centre in Lugogo, and drove past Kololo Airstrip almost every day.