There can always be some checking that happens as part of creating a new account.

Remember that to be effective, the follower needs to be able to find the new account when the old one is closed. They will do this by searching for an obvious keyword (in this case TurMedia or IslamicState), so checking the username against a block list of known terms previously used by terrorists should catch it.

For example, FB has a real names policy - try opening a FB account with a stupid name and see what happens - its not that hard.