Gregory's ServerMigration from X: "Migration in this context means that you used X/Twitter until a point in time and then immediately shifted to using Mastodon."
I had a trial phase where I kept my Twitter account for a while, before later deleting it. So while I would normally answer "yes", I did migrate from Twitter to Mastodon, because of the "immediately", I'll have to answer "no". Not sure why you stress the "immediately", I find that a bit weird.
@dj3ei @palllyyy yeah i think that question might not yield very useful results because it was both hard to understand and doesn't map neatly to most people's migration stories.