That is not what happened.

When the Lemmy software was first created, the original Hexbear (it had a different name, then) created a fork. A development or two down the line and the two forks were incompatible. The Hexbear devs started working on a fix long before the Reddit API-debacle exodus. It wasn't easy because the fork added features that were incompatible with, let's say, vanilla Lemmy until recently. The Hexbear devs eventually made the fixes, which made federation possible again. And the long-planned re-federation occurred. The timing is a coincidence.

As for federation, Hexbear asked it's community which instances should be federated. To maintain the friendly culture of Hexbear, there was an agreement to only federate with a few instances. Before that happened, dotworld defederated preemptively. Since then, I have no idea whose federated or defederated with who because I quickly lost interest with the drama.

I should say that I'd never used Hexbear before federation with my instance. I learned all this because it's publicly available knowledge. After federation, with all the drama, I searched 'federation' and some similar search terms on Hexbear communities and learned what I've just explained. The key point is that you don't need a conspiracy theory to explain motives for and the chronology of federation because, like the modlogs, the relevant conversations are still available to read.