A bit blurry or not, Plant and Page look pissed off indeed! Not that you can blame them...no wonder when the show continued Plant practically spat out the words to "Battle Of Evermore" and they just sort of zipped through the rest of the performance, wanting to get the hell out of there.
Yes, a bit of momentum was definitely lost when that happened, and without checking first, I think we lost a song or two, from the normal set list, as a result. Who can blame them for wanting to 'get gone'?!
Did the lectures/warnings given to the audience have any effect? Did they stop moving around and settle down after the bottle incident?
There was a short period where things calmed down, but I think it had more to do with them performing the acoustic set, than anything else. But the jostling to get closer, by some from the back would continue to cause small surges and irritation for people...
The crowd surging you describe sounds scary as hell. When you consider an incident like the Pearl Jam festival show where the kids got crushed (Roskilde? Back in the nineties, I remember that) it's amazing incidents like that didn't happen back in the seventies (The Who's infamous 'Cincinatti Incident' took place at the venue entrance). I've been to a couple of concerts where the crowd on the floor was in constant motion like that (AC/DC back in '91 for example) but it just goes to show how much concert security has changed over the years.
Yes, having lived in that area [near Ohio], I would often travel to different cities to see people perform, and after the incident at that Who show, I would often think long and hard about attending general admission shows at such big venues. I was never a fan of that change: going from reserved seats, which were on the floor - to the wide open "pit" of the general admission arrangement.
I always preferred the set-up where there was a "limited capacity" general admission area, at the lip of the stage, with a reserved seating area for the remainder of the floor area.
It justs makes for a safer experience for those who just want to enjoy the performance with decent sight-lines & a little breathing room; and for those who are fanatic enough [and have the money], the area just below the stage is for them.
I can remember attempting to take photos, once again from the audience, at a stadium show at Cleveland Municipal Stadium....The Stones were headlining.
My original position on the football field [this was the Cleveland Browns' home, at that time], was at about the 50 yard-line, where the sound was more or less listenable...
From the time band hit the stage, and had finished the opening song, I began to move up to get a better angle to take photos from, and the surge from the rest of the crowd pushed us forward so fast, that at one point, I nearly had my camera smashed against the security wall, at the lip of the stage.
Elbows flying, people pushing from behind and me trying to get a stable position to focus from, just didn't allow pictures to be taken on that occasion - not if you valued your personal health, anyway.
The eight hour drive resulted in something like 10 frames taken on that date - and my camera remaining in one piece, since I decided to haul my behind back to mid-field for the rest of the show.
After that, I rarely attended festivals or indoor festival "seating" shows any longer. Instead, I tried going to more club shows, and seeing new bands as they made their fame and fortune, in a smaller setting

We've all got stories to tell from different shows like this, I'm sure: funny, weird, or frightening......
And, yes, concert security has changed quite a lot, but the "bottom line" for the promoters has remained the same: squeeze as many people in, as possible, and rake in the cash, in the process.