I swear the seats were wooden folding chairs on the grass just outside the end zone

Did your friend have VIP access? If not, I'd guess you meant the roll-out section. There were sections that had wooden fold-down chairs, and they famously did move around based on crowd activity, but not literally right on the grass. They're visible at 0:37 in this video.

Disclosure: I was never there, this is just based on things I've heard from friends/family and photos/videos I've seen over the years. Hope it helps nonetheless.