Yes, I am very sure. There is no path behind the chopper, just a ledge on the left hand side. I'm not even sure we're having the same bug, no enemies actually spawn nearby, there's just a lot of floating un-manned guns firing bullets at invisible targets.
when you head into the area where the chopper is on the ground turn left theres a road there follow it around and it leads down into an area with a dead soldier and a dogtag infront of a portable building behind and to the left of that is a sewer tunnel go thru it and it will end the level.