The peak of the Mastodon migration was mid November, reportedly around 400k per week. This sounds like a lot, however a) many have moved back to Twitter due to it not being what they expected and b) Twitter has over 300m monthly active users.
Regardless, < 1% is not a lot of Twitter users by pretty much any stretch. I think people in tech or fringe communities are seeing a high uptake in their own groups and assuming that to be reflective of Twitter users at large.