There's a small cinder oval in the northwest part of Central Park, maybe 300 meters. Useful for speedwork now and then. I once was doing that when a group with a coach came and started jogging in the inside. I shouted "Track" to get them out of the way. Their coach, an Olympian from down-under, said "Take it easy Mate". If someone like that is so lackadaisical, what can we expect from others?
I think the OP ran into an usual situation and might have handled it better, but even were she to have asked the people to keep lane 1 clear what are the chances that someone wouldn't wander right in front of him? Would you take that risk? Of course she was pissed but it seems like something with no great solution other than simply going around the group when needed and staying in lane 1 when not, adding some meters to each lap. In a pre-race workout do you really care about precision, as opposed to feel? I can see her getting madder and madder as more and more people showed up.
There are times when the track is going to be too crowded, so I avoid it. Generally, though, as I'm warning up (always to the outside, sometimes clockwise) I'll go up to people and ask that they keep lane 1 open, and most do and I thank them when I'm done. It even can work at Bronxville's track, in which lane 4 is effectively lane 1 -- it's a bit over 400 meters -- and folks will keep lane 4 clear and I tell them why I'm there ("because the track is short").