"Controlled" because it probably was a deliberate attempt to burn out accumulated uncombusted fuel and lube oil in a location where secondary fires weren't likely to happen. GEs are more likely to need to be decoked than EMDs unless the EMDs have bad rings or seals and haven't been worked hard in a bit.
A few years back, I was on I-290 by Union Station and GRWO was working hard around the curve and also doing a good Vesuvius impression. Increasing the spectacle was that it was at night, like the photo.
Check MEC407's avatar for a daylight GE eruption.