It appears all 5 voters suggested Super User, yet the question was not migrated, but put "on hold".
The votes it received are not votes to migrate. They are simple off-topic votes. The dialog is the following:
The users have chosen the first option, which simply puts the question on hold and includes the message you noticed.
The option at the bottom leads to the migration dialog. That would have lead to actual migration should all users have chosen to migrate the question to Super User.