The bench is likely too far away from Oak Road CCTV for 'the four' to see or hear anything at the point they were being filmed. If you're thinking of 'running man' in particular, sounds could carry in the open at that time of night, but there's also a constant 'whirring' sound from all of the industry in the area.
As for access, I suspect that the bench is just beyond the park's main car park - which is locked up at night. There is foot access to the right, here:
Google Maps
@Joelle88 tells me there is also access to the left of the car park.
I may go for a walk around some of the sites of interest over the next few days. I know
@Strontium69 made some very good videos, but I'm happy to take requests such as photos or observations.