I was playing through 343 guilty spark on legendary, and I got to the part where to meet the dozen marines at the surface. Well we started moving, and I noticed there were 3 other yellow dots and machine gun fire in a different place to my marines. I figure that some marines had taken a detour. But then, out of a bush, comes Sergeant Johnson and two other marines. He then said "Glad to have your help Chief" or something like that. This was really surprising, because out of about 8 times I have played through the game, this has never happened. This only happened on the first time I played through on legendary.
I know about the whole random Sergeant Johnson appearances, but this takes the biscuit. I think Bungie added this special appearance in for legendary, to explain how he escaped. But has anyone had anything similar happen?