Same team, performing a big refactoring and significant improvement and modernization of some bits that were outdated and difficult to improve without a controlled demolition and rebuild.
The analogy breaks down, of course, because the governance didn't change, the project's relationship to its corporate backer wasn't standing in the way of progress, etc. (Except, I guess, that it might have gone faster if we'd had more money to hire more devs? But some of this was just a slog through a very old codebase with a lot of scar tissue, and it's hard to speed that up by putting more hands on it.)
Everything in npm 5 was literally planned years in advance. When we have this many people depending on a thing, we have to be careful about how we make drastic changes. Yarn was a strong signal from the community that we were on the right track, but it only seems like a "catalyst" when seen from the outside. Correlation is not causation, even when it lands first.