Did you read post #3, or the article? They moved to seats that cost more (since they have extra legroom - a common option on many airlines these days) without paying for the upgrade.
I read that, they were still in economy.
I know, the airlines have started playing games even with economy seats, charging a little more for this one, a little less for that. Its annoying. I don’t think its all airlines, but certainly United. If you’ve bought a ticket on line lately you see it when you reserve your seat.
Like I say, many times on a half empty plane, we’ve swapped seats to make ourselves more comfortable, and on a normal airline with normal staff, that isn’t a problem.