Well, first of all, the claim has never been that only 5% of all Twitter accounts are fake. It's been that only 5% of what Twitter reports as monetizable daily

Well, first of all, the claim has never been that only 5% of all Twitter accounts are fake. It's been that only 5% of what Twitter reports as monetizable daily active users are fake. Twitter already filters out a great many users (include many of the fake/bot accounts) from this figure. Think about it in reverse - you find it unbelievable that if Twitter were lying so boldly about fake accounts that there wouldn't be more scrutiny. There is not scrutiny. Therefore, you should conclude that perhaps Twitter is not lying in the way you seem to believe.